Reproductive and developmental biology of Aleochafa bilineata Gyllen ha1 (Coleoptera: ~taphylinidae)

Reproductive and developmental biology of Aleochafa bilineata Gyllenha1 (Coleoptera: ~taphylinidae) BY Marie-Josee Gauvin A thesis submitted to the ...
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Reproductive and developmental biology of Aleochafa bilineata Gyllenha1 (Coleoptera: ~taphylinidae)

BY Marie-Josee Gauvin

A thesis submitted to the Faculty of Graduate Studies and Research in partial fulfillment of requirements of the degree of Master's in Sciences

Department of Natural Resource Sciences (Entornology) Macdonald Campus of McGill University Sainte-Anne-de-Beltevue, Quebec, Canada August 1998

@ Marie-Josée Gauvin 1998

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Abstract Entomology Reproductive and developmental biology of Akocharo bllheata Gyllenhal (Coleoptera: Staphylinidae)

In Quebec 11 840 kg of insecticides are used against the cabbage maggot, Delia radicum L. (Diptera: Anthornyiidae) each year. It is possible to decrease this quantity of insecticide by using natural enemies such as fungi, nematodes,

predators and

parasitoids. Aleochara

bilineata

Gyllenhal

(Coleoptera: Staphylinidae) is a natural enemy of the cabbage maggot. Adults of this species are predators of eggs and larvae of cabbage maggot and the first instar larvae are ectoparasitoids of cabbage maggot pupae. A. bilineata oviposits its eggs in the soil, near plants infested with cabbage maggots. Differences in size have been noted in the eggs of A. bilineata. In insects several factors can affect egg size. Certain females can oviposit small trophic eggs which serve as food for emerging larvae or egg size can be affected by factors such as size and age of fernale, as well as, food and host quality. These factors have been studied in A. bilineata in order to determine the conditions that favor the production of small eggs. There is an increase in size and number of eggs oviposited by females that have access to food either with or without the presence of hosts. However, these eggs do not have a better hatching rate than eggs oviposited by unfed females. The age of females also affects the egg size laid. A. bilineata eggs are hydropic (absorption of water from their environment)

and increase in volume between 30 to 50 hours of development. Using scanning

and transmission electronic microscopy. the modifications in the egg envelope morphology have been followed during hydropy. The endochorion, which is very

dense and regular before swelling, becomes fragmented after swelling forming a mosaic pattern. Variation in larval weight may influence suwival thus affecting the reproductive success of the fernale. To evaluate the fitness of first instar larvae three parameters have been used: longevity, walking rate and searching capacity in relation to larval weight. Large larvae lived longer, walked faster as well as found and parasitized hosts more rapidly than small larvae. Based on these results we can conclude that large larvae have a better fitness than srnall larvae.

Résume MScm

Entomologie

Biologie de la reproduction et du d6veloppement chez Aleochara bilheaa Gyllenhal (Coleoptera: Staphylinidae) Chaque année au Québec, 11 840 kg d'insecticides sont utilis6s contre la mouche du chou, Delia radicum L. (Diptera: Anthomyiidae). II est possible de diminuer cette quantité d'insecticides en utilisant des ennemis naturels comme les champignons, les ndmatodes, les prédateurs et les parasitoïdes. Aleochara

bilineata Gyllenhal (Coleoptera: Staphylinidae) est un ennemi naturel de la mouche du chou. Les adultes de cette espèce sont prédateurs des oeufs et des laives de la mouche du chou et le premier stade larvaire est un ectoparasitoïde des pupes de cette même mouche. A. bilineata pond ses oeufs sur le sol près des plants infestés par la mouche du chou.

Des différences dans la taille des oeufs de A. bilheata ont Bte observées. Chez les insectes, plusieurs facteurs peuvent affecter le volume des oeufs. La femelle peut pondre des petits oeufs trophiques qui serviront de nourriture pour les larves qui auront Bmerg6 ou la taille des oeufs peut être affectde par la grosseur et l'âge de la femelle ou la qualit6 de l'hôte et de la nourriture. Ces facteurs ont BtB Btudids chez A. bilineata pour determiner quelles sont les conditions qui favorisent la production de petits oeufs. Les femelles qui ont accès

à la nourriture (en prdsence ou absence d'hôtes) pondent plus d'œufs et des œufs plus gros que les femelles non nourries. Par contre, ces œufs plus gros n'ont pas un meilleur taux d'6closion que les petits œufs. L'âge de la femelle affecte aussi la grosseur des œufs. Les oeufs de A. bilineaîa sont hydropiques (absorption d'eau durant leur développement) et, après 30 heures de d6veloppement, ils augmentent en volume jusqu'à 50 heures. En utilisant la microscopie Blectronique à balayage et

à transmission, nous avons observe les modifications à la morphologie des enveloppes de l'oeuf durant le phenornene d'hydropie. L'endochorion, qui est très dense et r6gulier avant le gonflement, devient fragmente à l'apparence d'une mosaïque après le gonflement. La variation dans le poids des larves peut influencer leur survie et par le fait même affecter le succès reproducteur de la femelle. Pour évaluer le fitness des larves de premier stade, trois paramètres ont été utilises: la longévité, la vitesse de marche et la capacité de recherche en relation avec le poids de la larve. Les grosses larves ont une longévité plus longue, marchent plus vite et trouvent et parasitent l'hôte plus rapidement que les petites larves. Donc. nous pouvons conclure que les grosses larves ont un meilleur fitness que les petites larves.

Remerciements Acknowledgments

J

e voudrais remercier mon directeur de recherche Dr Guy Boivin pour son support, son expertise, sa disponibilité et surtout pour sa patience. Un

énorme merci

Danielle Thibodeau du laboratoire d'entomologie

d'Agriculture et Agro-alimentaire Canada (St-Jean-sur-Richelieu) pour son aide constante lors de mes expériences, avec mes élevages, pour sa disponibilité et pour son support. Merci beaucoup au Dr Lucie Royer pour m'avoir transmis ses connaissances en entomologie plus particulièrement sur Aleochara biiineata et de s'être montrée aussi disponible pour répondre a mes questions et résoudre

mes problèmes.

u

n gros merci au programme de coopération scientifique et technologique franco-québecois pour mon stage effectué a l'université de Rennes 1 en France. Merci au Dr Jean-Pierre Nénon du laboratoire d'écobiologie des

insectes parasitoïdes de m'avoir accueilli, de m'avoir supervisé dans mes recherches au cours de ce sejour et d'avoir et6 et d'être toujours disponible pour mes questions. Merci à toutes les personnes qui m'ont permis de travailler efficacement et rapidement durant mon séjour: Joe Le Lannic (microscopie électronique

a

balayage), Jean-Paul Roland (microscopie électronique à

transmission), Marie-Rose Allo (microscopie Blectronique à transmission et fixation des Bchantillons), Frédéric Obé (développement des photos prises en microscopie), Dr Xavier Langlet (photos utilisees dans cette thèse et pour nos discussions), Dr Georges Vannier et Dr Georges Chauvin pour leur discussion.

M

erci au Dr. Daniel Cormier pour m'avoir aide dans mes analyses statistiques, pour ses nombreux conseils et ses encouragements. Merci à Dr. Cldment Vigneault pour s'être d6vou6

adapter le programme

d'analyse d'image pour la vitesse de marche des larves et ses nombreux conseils. Merci a Bernard Panneton pour le programme d'analyse des donndes.

Merci à Laetitia Laine et Nicole Simard pour leur aide durant mes expériences et pour avoir compile les donnees sur ordinateur. Merci à François Fournier pour sa disponibilité et la revision du chapitre 4.

T

hanks to Dr Robin K. Stewart from Natural Sciences Department at University of McGill (Campus Macdonald) for his correction, help in English

and his patience. Thanks to Marie Kubecki from Natural Sciences Department at University of McGill (Campus Macdonald) for her guidance and her patience.

M

erci à Annie Tardif pour avoir entendu et réentendu mes protocoles, mes

séminaires et les problèmes qui sont survenus durant ma maîtrise. Merci beaucoup pour son soutien, son temps et son ordinateur. Merci à Jean

Marsolais pour son aide et sa compr6hensionI pour les derniers milles qui ont 616 difficiles,

M

erci à toute les personnes du laboratoire d'entomologie à Agriculture et

Agro-alimentaire Canada (St-Jean-sur-Richelieu) pour leur soutien et leurs encouragements (David Biron, Julie Frenette, Daniel Gingras,

Claude Godin, Lise Lachance, Martine Lagac6, Caroline Roger, Josiane Vaillancourt).

u

n million de mercis à toute les personnes de ma famille et mes amis (es) pour leur support, leurs encouragements et d'avoir cru en moi. Merci à Roch Chenel, Isabelle Demers, Nancy Drolet, Ghislain Dub6, Etienne

Gauvin, Harold Gauvin, Jonny Gauvin, Eve-Lyne Lamontagne, Mariette Lloyd (correction de l'anglais), Nathalie Masse, Karine Sergerie et tous les autres. Et finalement un &nome merci é ma petite maman (Ginet Gauvin) pour son support.

A la vie ...

Table of contents Abstract .................................................................................................................. i

...

Résume.................................................................................................................III Remerciements (Acknowledgments) .....................................................................v

Table of content.................................................................................................... vii List of figures .........................................................................................................xi List of tables..........................................................................................................xiv

INTRODUCTlON

..................................... ...........................m............. 1

f hesis format ...................................................................................................4 References ....................................................................................................... 5

CHAPTER 1: LITERATURE REVlEW

...............................................6

1 . Reproductive strategy in insect........................................................................7

1.1 lnvestrnent in eggs ............................................................................. 7 1.1.1 Ice Box Hypothesis...............................................................................7 1.1.2 Egg size ................................................................................................9 1.1.3 Hydropy ...............................................................................................10

1.2 Fitness of larw ........................................................................................... 12

2. Aleochara bilineata Gyllenhal (Coleoptera: Staphylinidae) ............................... 14

....... 2.1 Distribution and life history of Staphylinidae ..........................

. . . . 14

2.2 Distribution and life history of Aleochara spp ..............................................15 2.3 Evolution of Aleochara spp.................................................................... 16

2A.Morphology and biology of Aleochara bilheata .......................................... 17 2.4.1 Adult .................................................................................................... 17 2.4.2 Egg ..................................................................................................19 2.4.3 First instar lama ...................................................................................20

2.4.4 Second instar lama............................................................................. 2 2 2.4.5 Third instar Iawa................................................................................. 2 2

2.4.6 Pupa ................................................................................................... -23 vii

2.5 Geographical distribution ...........................................................................2 4

3. Delia radicum L. (Diptera: Anthomyiidae) ........................................................25 3.1 Morphology................................................................................................ 25 3.1.1 Adult ....................................................................................................25 3.1.2 Egg ...................................................................................................... 25 3.1.3 Larva ...................................................................................................26 3.1.4 Puparium .............................................................................................26 3.2 Biology ........................................................................................................ 27

3.3 Geographical distribution ...................................................................... 2

8

3.4 Control ........................................................................................................ 28 3.4.1 Cultural control .................................................................................... 28 3.4.2 Chernical control.................................................................................. 29 3.4.3 Biological control .................................................................................29

References ........................................................................................................... 32 Figures.................................................................................................................. 43

59 Tables ...................................................................................................................

CHAPTER 11: IMPACT OF FOOD AND HOST AVAlLABlLlTY ON SIZE AND SURVIVAL OF EGG OF ALEOCHARA

BlLlNEATA

GYLLENHAL

STAPHY LINIDAE)

(COLEOPTERA:

................................................

63

Abstract ..........................................................................................................64 introduction.......................................................................................................... 65 Materials and methods ......................................................................................66

..

General conditions............................................................................................66 Oviposition strategy according to host and food availability............................

67

viii

Presence of trophic eggs ............................................................................... 68 Influence of host and food availability ...............................................................68 Discussion ........................................................................................................... 69 References ........................................................................................................... 72 Figures..................................................................................................................75 Connecting text ...................................................................................................7 9

CHAPTER 111: DEVELOPMENT AND ENVELOPE STRUCTURE OF

ALEOCHARA

BlLlNEATA

GYLLENHAL

(COLEOPTERA: STAPHYLINIDAE) EGGS

..........80

................................................................................................................ 81 Introduction ........................................................................................................... 82 Materials and methods ..................................................................................... 8 5 Egg size and weight .........................................................................................85 Morphology of egg envelope ............................................................................86

Abstract

Statistics ........................................................................................................... 87 Results and discussion ......................................................................................... 88 Change in egg volume with time......................................................................8 8 Weight variation in time .................................................................................... 88 Morphology of egg envelope ...........................................................................9 0 References ........................................................................................................... 94 Figures.................................................................................................................. 98 Connecting text .................................................................................................... 112

CHAPTER Ilk EFFECT OF SIZE ON FITNESS IN THE LARVAE OF

ALEOCHARA

BILINEATA

GY LLENHAL

...... . . . ....... 113

(COLEOPTERA: STAPHYLINIDAE)

Abstract .............................................................................................................

114

Introduction.......................................................................................................... 115 Materials and methods ........................................................................................ 117

.................................................................1 17 General conditions...................... . Longevity .........................................................................................................118 Walking rate..................................................................................................... 118 Searching capacity .......................................................................................... 118 Statistics ..........................................................................................................119 Results and discussion .......................................................................................120 Longevity .........................................................................................................120

Waiking rate..................................................................................................... 121 Searching capacity .......................................................................................... 122 Impact of size of fitness ...................................................................................122 References .......................................................................................................... 124

Figures.................................................................................................................127

References ...................................................................................................... 137

List of figures Figure 1.1: A- Aleochara bilineata and 6- A. bipustulata showing red spots on its

elytra (Taken frorn Langlet, 1997) (Scale bar = 2 mm) ....................43 Figure 1.2: A- AIeochara bilineata feeding on Delia radicum eggs (Taken from

Langlet, 1997) (Scale bar = 2 mm). 8- Mating behavior in Aleochara

bilineata where the male bends its abdomen over its head and its claspers are extruded (Taken from Langlet, 1997) (Scale bar = 2

mm) .................................................................................................45 Figure 1.3: A- Egg of Aleochara bilineata before hatching showing the visible eye

spots and mandibles (Taken from Langlet, 1997) (Scale bar = 0.1

mm). B- First instar larva of Aieochara bilineata (Taken from Langlet, 1997) (Scale bar = 0.2 mm) ........................................................4 7

Figure 1.4: Pupa of Delia radicum parasitized by Aleochara bilineata with the

entry hole of the parasitoid larva and the first instar of A. bilineata visible through the puparium (Taken from Langlet, 1997) (Scale bar = 1 mm) ............................................................................................ 49

Figure 1.5: Nymph of Aleochara bilineata A- early stage and B- later stage

(Taken from Langlet, 1997) (Scale bar = 1 mm) ..............................51 Figure 1.6: A- Male and B- fernale of Delia radicum (Taken from Langlet, 1997)

(Scale bar = 2 mm) ......................................................................... 53 Figure 1.7: Eggs of Delia radicum (Taken from Langlet, 1997) (Scale bar = 0.5

mm) ................................................................................................5 5 Figure 1.8: A- Lama of Delia radicum (Scale bar = 1 mm). 6- Pupae of Delia

radicum (Scale bar = 2 mm) ........................................................... .57 Figure 2.1: Distribution of egg volume produced by Aleochara bilineata over a

period of 15 days by A- 7 fed couples with hosts, 6- 7 fed couples without host and C- 6 unfed couples with hosts ...............................75

Figure 2.2: Oviposition cycle over 15 days for females of Aleochara bilineata according to treatments ( - :8 fed couples with hosts ,

-:10

-:10 unfed couples with hosts). Day one being the first day where the female laid ...........................77

fed couples without host and

Figure 3.1:Ternporal variation of egg volume (+ SD) in Aleochara bilineata at

20%.

................................................................................................98

Figure 3.2: Fresh and dry weight (* SD) of Aleochara bilineata eggs before ( 1

+

1 hour) A- and after (68 k 1 hours) 6- swelling at 20°C. " Pc0.0001 (Student test) ................................................................................100

Figure 3.3: A- General view of an oocyte of Aleochara bilineata. Scale bar = 100 pm. 6- Detail of the surface of an oocyte of Aleochara bilineata. Scale bar = 1 prn ......................................................................... 1 02

Figure 3.4: Oocyte of Aleochara bilineata with follicular cells (FC), granules (G) and vitellus (V). A- Young oocyte with follicular cells and many granules. Scale bar = 5 p m 6-Old oocyte with follicular cells. Scale bars = 5 pm.................................................................................104

Figure 3.5: A- Aleochara bilineata egg 24 hours-old with fungus (F), mineral particles (P) and bacteria (B). Scale bar = 10 prn. B- Egg 24 hoursold of A. bilineata with granules (G) and spermatozoids (S). Scale bars = 1 pm. C- A. bilineata egg 24 hours-old with granules (G) and mineral particles (P). Scale bar = I p m 0- General view of eggs 24 hours-old of A. bilineata. Scale bar = 100 pm. E- General view of egg

seven days-old of A. bilineata with larva present (L). Scale bar = 1OOpm............................................................................................. 106

xii

Figure 3.6: A- Egg envelopes of Aleochara bilineata 1 hour after oviposition. Presence of granules (G) in exochorion (EX). EN = endochorion. Scale bar = 5 Fm. 6- Egg envelopes 17 hours-old. The exochorion

(EX) is irregular. EN = endochorion. V = vitellus. VM = vitelline membrane. Scale bars = 1 Pm. C- Egg envelopes 30 hours-old. Exochorion (EX). Endochorion (EN). Vitellus (V). Vitelline membrane (VM). Scale bar = 3 pm. ..................................................................108 Figure 3.7 A- Egg envelopes of 40 hours-old Aleochara bilineata eggs. The

endochorion (EN) is fragrnented. The serosal cuticle (SC) is formed of several layers. EX = exochorion. E = embryo. Scale bar = 5 Pm. 8Egg envelopes of 6 days-old egg. Presence of granules (G) in

exochorion (EX). EN = endochorion. Scale bar = 3 Fm. CTransverse view (SEM) of egg envelopes of 6 days-old egg. EX = exochorion. EN = endochorion. VM = vitelline membrane. Scale bar

= 1 Pm. 0- lnside view (SEM) of fragmented endochorion of 6 days1 10 old egg. Scale bar = 1 pm. .............................................................

Figure 4.1 : Schematic representation of the experimental setup ......................127 Figure 4.2: Distribution of weight of 185 larvae of Aleochara bilineata 30

I30

minutes after hatching .................................................................129

Flgure 4.3: Percentage of small and large Aleochara bilineata larvae that did not find a host. found a host but did not penetrate and found a host penetrate after a period of 48 hours................................................131

List of tables Table 1.1: Groups of animals where cannibalism behavior is known (Fox. 1975;

Elgar & Crespi. 1992) ....................................................................5 9 Table 1.2: Synonymy

references

of

Aleochara bilineata

Gyllenhal

(1810)

..................................................................................

and 60

Table 1.3: Length and width of Aleochara bilineata eggs according to authors ..61 Table 1.4: Lifetime and details consumption of preys by Aleochara bilineata by

different authors ...............................................................................61 Table 1.5. Synonymy of Delia radicum L. according to regions and authors......62

xiv

INTRODUCTION

In Quebec, cruciferous crops such as cabbage, Brussels sprouts, cauliflower and broccoli are important as they occupy an area of 4 893 ha. These crops represent 36 million dollars at harvest (Statistiques Canada, 1998). These crucifers are attacked by several pests: Lepidoptera (Plutella xylostella L.,

Artogeia rapae L. and Trichoplusia ni Hübner), Coleoptera (Phyllotreta cNciferae Goeze, P. robusta Leconte, P. siriolata F., P. albionica Leconte and Entomoscelis americana Brown), Dermaptera (Forficula auricularia L.) , Homoptera (Brevicoryne brassicae L. and Lipaphis erysimi Kaltenbach) and Diptera (Delia radicum L.) (Godin, 1997; Richard & Boivin, 1994). ln Quebec, 11 840 kg of insecticide are used against the cabbage maggot, D. radicum L.

(Diptera: Anthomyiidae), each year. This represents 9% of al1 insecticides used in Quebec (Chagnon & Payette, 1990). Young plants are preferred oviposition sites for cabbage maggot females. When attacked, cabbage plants either grow more slowly or die, which affects total yield. To decrease this quantity of insecticides and keep a control on the cabbage maggot, several natural enemies can be used including Aleochafa bilineata Gyllenhal (Coleoptera; Staphylinidae). A. bilineata adults are predators of cabbage maggot eggs and larvae while first instar larvae are ectoparasitoids of pupae. In the literature, little data is available on factors affecting the oviposition behavior of the female, the developmental biology of eggs and the larval efficiency of Aleuchara bilineata. Several reproductive strategies can be used by insect females to increase their fitness at the individual and species level. At the individual level, the female can oviposit sterile eggs that serve as food for larvae. It can also invest different quantities of resources in eggs according to environmental and physical conditions. At the species level, the female can oviposit numerous small eggs containing few resources. These eggs need to absorb oxygen, nutrient or water from their environment to complete their development. In this thesis these three strategies are examined to understand the oviposition behavior, the developmental biology of eggs and the impact of this investment in eggs on the larval fitness.

A. bilineata female oviposits a large range of egg sizes. Our first objective was to determine the conditions in which these small and large eggs were oviposited. The Ice Box Hypothesis where the female oviposits sterile trophic eggs when resources are scarce (Alexander, 1974) has been tested. The impact of availability of food and host as well as female age and site on the oviposition

of A. bilineata have been studied. This is to discover whether these factors permit the production of small eggs. The second chapter deals with the reproductive strategy at the species level ( M e investment in small eggs) and the developrnental biology of these eggs of A. bilineata. Our first objective was to detemine the change in egg volume over time. Our second objective was to prove the morphological reason for this increase in s i m . We hypothesized that the egg absorbs a certain quantity of water during its development (hydropy). We then compared fresh and dry weight of eggs before and after swelling and also examined the modification of egg envelopes during swelling with scanning and transmission electronic microscopy. At emergence, different weights of larvae have been measured. The last

chapter investigates the efficiency of larvae by measuring the fitness of large and small larvae. Three parameters have been used to evaluate larval fitness. The first includes longevity whereby the lawa is followed from emergence until death. The second parameter consisted of walking rate white using an image analysis system. Finally we determined the searching capacity of larva when it was in the presence of pupa for a period of 48 hours.

Thesis format

"Candidates have the option of including, as part of the thesis, the text of a paper(s) submitted or to be submitted for publication, or the clearly-duplicated text of a published paper(s). These texts must be bound as an integral part of the thesis. If this option is chosen, connecting texts that provide logical bridges between the different papers are mandatory. The thesis must be written in such a way that it is

more than a mere collection of manuscripts; in other words, results of a series of papers must be integrated. The thesis must still conform to al1 other requirements of the "Guidelines for Thesis Preparation". The thesis rnust include: A Table of Contents, an abstract in English and French, an introduction which clearly states the rationale and the objectives of the study, a comprehensive review of the literature, a final conclusion and summary, and a thorough bibliography or reference list. Additional material must be provided where appropriate (e.g. in appendices) and in sufficient detail to allow a clear and precise judgment to be made of the importance and originality of the research reported in the thesis. In the case of manuscripts CO-authoredby the candidate and others, the candidate is required to make an explicit statement in the thesis as to who contributed to such work and to what extent. Supervisors must attest to the accuracy of such statements at the doctoral oral defense. Since the task of the examiners is made more difficult in these cases, it is in the candidate's interest to make perfectly clear the responsibilities of al1 the authors of the CO-authored papers. Under no circumstances can a CO-authorof any component of such a thesis serve as an examiner for that thesis." The third chapter Developmental and envelope structure of A/eoch~ra

biineata Gyllenhal (Coleoptera: Staphylinidw) eggs will be submitted to Int. J. lnsect Morphol. & Embyol., CO-authoredby the candidate's supervisor Dr G.

Boivin and the candidate, Dr J.P. Nenon. Dr G. Boivin and Dr J.P. Nenon provided supervision, read and revised the manuscript. The fourth chapter Effect of size on fitness in the lawae of Aleochara bilineata Gyllenha1 (Coleoptera: Staphylinidse) will be submitted to Oikos, COauthored by the candidate's supervisor, Dr G. Boivin. Dr G. Boivin provided supervision, read and revised the manuscript.

References Alexander, RD. 1974. The evolution of social behavior. Annu. Rev. Ecol. Syst. 5 : 325-383.

Chagnon, M. & A. Payette. 1990. Modes alternatifs de repression des insectes dans les agro-ecosystemes québécois. Tome 1 : Document synthbse. Ministère de l'Environnement et Centre québécois de valorisation de la biomasse. Quebec. 81 p.

Godin, C. 1997. Seasonal occurrence and parasitism of Lepidoptera pests of crucifers, and host age selection by a potential control agent:

Trichogramma. Macdonald Campus of McGill University. Department of natural resource sciences (entomology). 144p. Richard, C. & G. Boivin. 1994. Maladies et ravageurs des cultures légumières au Canada. La SociW Canadienne de Phytopathologie et la Soci6t6 d'entomologie du Canada. Ottawa. 590 p.

Statistiques Canada. 1998. Production de fruits et ldgumes. Février. Vol. 66. No. 2.

CHAPTER 1 LITERATURE REVIEW

1. REPRODUCTIVE STRATEGY IN INSECT lnsect adults use several reproductive strategies to increase their fitness. These strategies can be at the species level. An example of this is spatial strategies whereby males or females either disperse to copulate thus decreasing the probability of inbreeding or copulate at emergence without dispersal therefore gaining time especially in time-limited species. The strategies can be visual, where males and females aggregate in swarms to copulate, again saving time (Wickman & Jansson, 1997). The resources that a female invests in eggs will vary between species. While some species oviposit a few eggs that are rich in

resources, other species oviposit numerous small eggs containing little resources (hydropic eggs). These hydropic eggs will absorb water, nutrient or oxygen from their habitat (Smith & Frehvell, 1974; McGinley et al., 1987). Within a species, individual females may either oviposit most of their eggs in one or few sites, or disperse them in several sites (Berger, 1989; Elgar & Crespi, 1992). A female can oviposit sterile eggs to serve as food for larvae (Ice Box Hypothesis) or invest different quantities of resource in eggs depending of environmental and physical conditions (Alexander, 1974). In this literature review three strategies will discussed. The two firsts are at individual level (Ice Box Hypothesis and egg size) and the third is at species level (hydropic egg).

1.1 lnvestment in eggs 1.1.1 Ice Box Hypothesis

Elgar and Crespi (1992) define cannibalism as eating conspecifics, which

are either dead or alive prior to the interaction. Cannibalism is a behaviour that rnay reduce population size before acute resource shortage causes severe

physiological stress (Fox, 1975). This behaviour has been reported in several groups of animals, induding insects (Table 1A). Elgar and Crespi (1992) divided

cannibalism into two categories: non-kin and kin cannibalism. In non-kin cannibalism, preyed individuals are not restricted to their own species. They may not even discriminate between conspecific and other preys. This type of cannibalisrn can be described more accurately as indiscriminate or incidental cannibalism (Elgar & Crespi, 1992). Kin cannibalism can be divided into filial and sibling cannibalism. Filial cannibalism is observed when a parent kills and consumes its own progeny, as in Nicrophorus vespilloides Herbst (Coleoptera: Siliphidae) (Elgar & Crespi, 1992). The aduits of this species oviposit egg clutches near vertebrate corpses that they have previously placed in a burial chamber or crypt. After hatching, the larvae migrate to the corpse and develop inside. The three laival instars are found insids the corpse and the insect pupates in the soil. Male and female are present during larval development to repair the chamber, feed the larvae and protect the clutch against predators. The adults eat up to half the offspring when food supply is limited. This serves to regulate the number of larvae in a corpse (Elgar & Crespi, 1992). Sibling cannibalism occurs when a larva eats an egg or a younger larva of the

same

clutch.

In

Plagiodeva

versicolora

Laicharting

(Coleoptera:

Chrysornelidae), the female oviposits egg clutches and the larvae form an aggregated feeding group that persist during the fint two instars. An egg clutch is almost exclusively laid by one female but the female may have had multiple mating. Therefore, the female laid groups of eggs contain both full sibs (brothers and sisters) and half-sibs (half-brothets and half-sisters). The larvae are very cannibalistic for a period of 24 hours after hatching and eat eggs from their clutch. After this period, the larvae are herbivorous. For an individual, it is advantageous to be cannibalistic as it insures a rapid growth. However on a group level, the advantages are less obvious. f hese larvae have social behaviors (feeding coordination, group defensive displays and synchronous molting) and there is a positive correlation between larval group size and survivonhip. Therefore, cannibalism is disadvantageous in terms of reduced group size.

Evolution should therefore select a frequency of cannibalism that reaches a balance between individual and group advantages (Breden & Wade, 1985). Some species may present more than one type of cannibalism. The milkweed leaf beetle, Labidomera clivicollis Kirby (Coleoptera: Chrysomelidae) exhibits three types of cannibalism. The first type is cannibalism of eggs by adult females (filial cannibalism). The second and the third type are sibling cannibalism where larvae eat either eggs or younger iarvae of the same ciutch. There is a positive correlation between clutch size and the proportion of eggs cannibalized. L. clivicollis oviposits an average of 15-17% of eggs which will never develop

embryos (Dickinson, 1992). These eggs, narned trophic eggs, are generally cannibalized along with some fertile eggs, and constitute ovarian-derived structures or fluids, homologous to fertile eggs (Elgar & Crespi, 1992). This phenornenon is further explained by the Ice Box Hypothesis which predicts that when the survivorship of offspring varies unpredictably, females may gain by increasing clutch size. As a result, when resources are abundant, al1 offspring may prosper but, when less resources are available, some offspring serve as food for others (Alexander, 1974; Elgar & Crespi, 1992). 1.1.2 Egg size

Variation in egg size can be explained by variation in female size or age, food quality or host quality (Karlsson, 1987; Berger, 1989; Fitt, 1990; Wallin et a/., 1992; Fox, 1993; Braby, 1994; Fox, 1994). For example, in Chi10 partellus

Swinhoe (Lepidoptera: Pyralidae) large females lay larger eggs than srnall females (Berger, 1989). In Pararge aegeda L. (Lepidoptera: Satyrinae) egg weight and oviposition rate decrease with female age (Karlsson, 1987). There are

several indications that there is a correlation between egg size and offspring performance (Wallin et aL, 1992; Fox, 1993; Braby, 1994; Fox, 1994). In Callosobnrchus maculatus F., (Coleoptera: Bruchidae), the larvae from large

eggs develop faster and emerge as larger adults in comparison to the larvae from

small eggs (FOX, 1994). In Pterostichus cupreus L. (Coleoptera: Carabidae), larvae from large eggs survive longer and hatch earlier than larvae from small

eggs (Wallin et ai., 1992). 1.1.3 Hydropy

lnsect eggs comprise several envelopes, which are either derived maternally or from the embryo. Two maternally derived envelopes secreted by follicular cells exist at oviposition time: the chorion and the vitelline membrane (8iemont et al., 1981; Chauvin et ab, 1988; Larink & Bilinski, 1989; Neveu et ab, 1997). The chorion is often composed of the exochorion and endochorion and can be covered by mucoproteins secreted by the accessory glands of the female. These proteins are used to secure the egg to the substrate and their presence

explains the development of bacteria on the egg surface (Chauvin & Chauvin, 1980; Biemont et al, 1981; Nénon et al., 1995). After oviposition other envelopes, secreted by the embryo, are added: the serosal and embryonic cuticles (Chauvin et al, 1973; Chauvin & Chauvin, 1980; Hinton, 198 1; Chauvin et ab, 1988). All envelopes are essential to protect the egg against hydric and

therrnic variations and predators however they also play a role in hydric and respiratory exchanges (Chauvin & Chauvin, 1980; Chauvin et al., 1988). In some species, females produce fewer eggs and their reproduction rate is reduced. However, more investment is placed in each egg. The rnortality rate is generally lower and these eggs do not need to absorb nutrients, water or oxygen. By investing more into each egg, the fitness of individual offspring increases (Smith & Fretwell, 1974; McGinley et al., 1987). In others species, females produce more eggs per unit of time thus placing a smaller investment in each egg. In such species, the rate of mortality is high but it is compensated by the fact that there are many eggs. These eggs, named hydropic eggs, can absorb nutrients, water or oxygen to complete their development. Many aquatic

and terrestrial eggs of Orthoptera, Heteroptera, Hornoptera, Coleoptera,

Hymenoptera and Diptera require water to develop (Hinton, 1981; Chauvin et al., 1991). The water absorbed is in a liquid phase and this absorption causes an

increase in the egg volume during its development. In hydropic eggs, the water is absorbed by three types of hydropyles or hygropyles (organs specialized for the absorption of liquid water (Hinton, 1981)): serosal hydropyles, serosal cuticle hydropyles and chorionic hydropyles. These hydropyles cells do not actively absorb water. However, they secrete a specialized form of serosal cuticle of the hydropyle and regulate its permeability to water (Hinton, 1981). Serosal hydropyles are present in some Orthoptera and Hemiptera and their usual position is at the anterior pole of the egg. Serosal cuticle hydropyles are known in Acrididae (Orthoptera) where two serosal cuticles are formed, the outer and the inner, and both take part in the formation of hydropyle at the posterior pole. There is a change in the permeability of the hydropyle cuticle: when diapause is initiated, the outer layer becomes impermeable. When diapause is completed, it becomes permeable to water (Hinton, 1981). Chorionic hydropyles are present in several orders such as Heteroptera, Homoptera and Coleoptera. The principal characteristic of these eggs is the presence of a respiratory air layer with aeropyles in the shell of the egg even if the egg is dried (Hinton, 1981). However, hydropyles have not been recognized in most eggs of Hymenoptera and Coleoptera that are known to absorb liquid water.

In general, insect eggs are in contact with liquid of osmotic pressure lower than that of the embryonic fluids and tissues. Thus, passive absorption occurs (osmosis) (Hinton, 1981). The absorption of liquid water often results in an increase in egg size and modification in the egg envelopes. Several acridids, mirid bugs and dytiscid beetles have a chorion that fragments during water

absorption (Hartley, 1961; Lincoln, 1961). In Dyfiscus marginalis L. (Coleoptera: Dyüscidae), the egg chorion splits during water absorption and the serosal cuticle serves to support and protect the developing eggs (Blunck (1914) in Lincoln, 1961). When the egg swells, in other insects, the chorion stays intact. In Ocypus olens Müller (Coleoptera: Staphylinidae) the chorion simply stretches when the

volume of the egg increases (Slifer, 1937; Lincoln, 1961). In Tetrix vittata Zetter (Orthoptera: Tetrigidae), the anterior horn appears as an expansion chamber allowing the egg to swell (Lincoln, 1961; Hartley, 1962).

1.2 Fitness of larva The fitness is a measure of the response of a population of organisms to natural selection. This is based on the number of offspring contributing to the next generation in relation to the number of offspring required to maintain th8 particular population constant in size (Abercornbie et al., 1980). The fitness has been used to indicate a measure of general adaptedness, and to indicate a shortterm measure of reproductive success (de Jong, 1994). However in certain kind of social behavior, such as altruism, certain traits with a low individual fitness can be favored by selection since these traits increase the population fitness (Queller, 1996).

The fitness of a fernale parasitoid depends on the environment and her constraints such as longevity, fecundity, host-finding ability and size. The sizefitness hypothesis proposes that fitness of female increases with increasing size (de Jong, 1994; Godfray, 1994; Visser, 1994; Kazmer & Luck, 1995). There are many measures to estimate the relationship between parasitoid size and fitness: egg load at emergence, egg size, longevity, searching efficiency on patches, travel speed... (Visser, 1994). For instance in cornparison to small females, in Aphaerata minuta Nees (Hymenoptera: Barconidae), larger females have more eggs available, larger eggs, live longer and have a higher searching efficiency

within patches (Visser, 1994). In gregarious parasitoids, adult size decreases as the number of developing progeny increases in similar-sized hosts. However in solitary parasitoid, adult size is positively correlated with host size (Kazmer & Luck, 1995). Moreover when the energy expended on individual offspring is incteased, the number of offspring that parents can produce is decreased. When the energy expended on individual offspring increases, the fitness of individual

offspring increases (Smith & Fretwell, 1974). Fitness applies to individuals, therefore fitness parameters can be measured in larvae (Wiklund & Persson, 1983; Fox, 1993; Braby, 1994). Braby (1994) has measured three fitness parameters in butterflies of the genus

Mycalesis. These parameters were lawal survival, larval developmental time and pupal weight in relation to egg size. Under field conditions, there is a correlation between egg size and offspring fitness suggesting that lawae from larger eggs

may do better than those from srnaller eggs. No rneasure of the fitness of A. blïineata larvae is available at the moment.

2. ALEOCHARA BlLlNEATA GYLLENHAL

(COLEOPTERA: STAPHYLINIDAE) 2.1 Distribution and life history of Staphylinidae There are more than 14 000 species of Staphylinidae (Coleoptera) worldwide (Eggleton & Belshaw, 1992) and in North America, nearly 2 900

species live in a variety of habitats. The majority of species live in decaying materials such as dung and carrion. Other species dwell under stones and other objects on the ground, along streams and seashores, in fungi and leaf litter and in nests of birds, mammals, ants and termites (Borror et al., 1954). Staphylinidae that are not scavengers can be predaceous or parasitoid. The Staphylinidae are characterized by short elytra and an elongate body. Beneath the elytra, large and fully functional wings are folded. The Staphylinidae have the habit of elevating their abdomen when disturbed. When they run, they frequently raise the tip of their abdomen, as do scorpions. The mandibles are very long, slender and sharp and are generally crossed in front of the head. Most

Staphylinidae are brown or black and measure about 25 mm in length (Borror et

a/., 1954). Many Staphylinidae that live as parasitoids attack pupae on or in the soi1 but occasionally some species find pupae on or in plants. For exarnple,

Maseochara valida Lec. attacks pupae of Copestylum marginatum Say (Diptera: Syrphidae), a syrphid fly that develops in the semiliquid material in the decaying leaves of cactus (Clausen, 1940; Eggleton & Belshaw, 1992).

2.2 Distribution and life history of Aleochm spp. The genus Aleochara Grovenhorst has about 300 species worldwide, (Klimaszewski, 1984); al1 species for which the life history is known, are parasitoids. In North America, the genus Aleochara is divided into seven subgenera: Coprochara Mulsant and Rey (A. bimaculata Gravenhorst, A. bilineata Gyllenhal and A. verna Say (synonymous of A. bipustulata L.)), Xenochara Mulsant and Rey (A. tristis Gravenhorst, A. lacertina Sharp, A. taeniata Erichson and A. puberula Klug), Aleochara Mulsant and Rey (A. curtula

Goeze and A. lata Gravenhorst), Emplenota Casey (A. /ittoralis Maklin and A. pacifica Casey) Calochara Casey (A. viltosa Mannerheim), Echochara Casey (A. lucifuga Casey) and Maseochara Sharp (A. valida Leconte). These species are parasitoids

of

Muscidae,

Anthomyiidae,

Calliphoridae,

Sarcophagidae,

Coelopidae, Sepsidae and Syrphidae, which are al1 dipteran species (Wadsworth, 1 915; Klimaszewski, 1984). In 1836, Say (in Wadsworth, 1915) described A. vema in America. Fortyfour years later, Sprague, in Europe, described A. nitida. He was the fint to discuss that Aleochara sp. emerged from a cabbage maggot pupae in his laboratory (Wadsworth, 1915). But Sprague did not find the hole by which the Staphylinidae could have entered the puparium: "thus proving beyond a doubt that either the eggs, or what seems more probable, the young larva of this Staphylinus (genus Aleochara) entered the fly larvae long before they had arrived at maturityu (Wadsworth, 1915). Fletcher (1890) was the first one to consider Aleochara sp. as a true parasitoid (in Wadsworth, 1915). A few years later, in 1894, Slingerland (in Wadsworth, 1915) mentioned an Aleochara attacking the cabbage maggot Delia radicum (Diptera: Anthomyiidae). This Aleochara was considered to be identical with A. nitida (Gravenhorst) which was identified by

Say in 1836.

Klirnaszewski (1984) revised the genus Aleochara. In these species, the lama is an ectoparasitoid within puparia of cyclorrhaphous Diptera where they undergo hypermetamorphism. The adults of these species are predators of the lama0 and eggs of the same Diptera species (Klimaszewski, 1984).

2.3 Evolution of Aleochara spp. The 1 600 species of Coleoptera parasitoids are distributed in 11 families. Thirteen acquisitions of the parasitoid lifestyle are necessary to explain these 11 families away which one acquisition for the 500 species of Staphylinidae that are parasitoid (Eggleton & Belshaw, 1992; Eggleton & Belshaw, 1993). Fuldner (1960) has proposed an evolutionary pathway for the acquisition of parasitic life

in Staphylinidae. Many Staphylinidae, including the genus Aleochara, are necrophagous, .aeding on animal corpses where dipteran larvae are present. Some necrophagous staphylinids have probably started to predate on these dipteran or other prey in the same habitat. In these adult predators living and developing in this habitat, the larvae specialized to become parasites of the same species pupae (Fuldner, 1960; Eggleton & Belshaw, 1992; Eggleton & Belshaw, 1993). Some species such as Aieuchara curtuia Goeze, A. intricata Mannh, A.

bilineata Gyllenhal and A. bipustulata L. evolved as ectoparasitoids and show polymetamorphism (Fuldner, 1960). In A. curtula and A. intricata, the first instar is campodeiform and enters the dipteran puparia to eat the pupa. The second and third instars are eruciforms whiie the third instar exhibits campodeiform behavior, because it exits the host puparium to pupate in the soil. Another group

b2f

species, including A. bilineata and A. bipustulata, are completely ectoparasitoid. Their third instar lawa is eruciform and pupates in the host puparium. For these species, the third instar larva is not able to live outside of host puparium. After feeding on the pupa, the third instar lawa spins its cocoon inside the host puparium. According to Fuldner (1960) the larval life of A. bilineata and A. bipustulata is an advanced form of parasitism in Dipteran pupae because the parasitoid pupates in the host.

2.4 Morphology and biology of Aleochara bilineata A. bilineata is a species in the subgenus Coprochara. The synonymy of

this species is presented in table 1.2.

2.4.1 Adult

The imago of A. bilineata is slender and shining black with short elytra lacking the spots found on the elytra of A. bipustulata L. (Figure 1 . 1 ). It abdomen is pointed and its wings are functional. The adult can fly at least five kilometers (Tomlin et al., 1992). The average site of the fernale is 5.81 mm, larger than the male that measures 5.40 mm (Colhoun, 1953). The male has an average of sixteen short sting-like bristles on the sixth abdominal tergum. However in females, there is an average of twenty bristles that are longer than those of males (Colhoun, 1953). Adults of Aleochara are predators of Diptera eggs and larvae (Colhoun, 1953; Read, 1962; Bromand, 1980) (Figure 1.2A). Upon biting the cuticle of Diptera larvae, A. bilineata ingests the haemolymph of its prey through a combination of lapping and sucking motions. According to Bromand (1980), a couple of A. bilineata under greenhouse conditions can eat approximately 2 400 cabbage maggot eggs or first instar larvae, or about 250 cabbage maggot third instar laivae in their lifetime. An adult feeding on eggs or one to two day old larvae destroys an average of 23.8 Diptera per day throughout its life. However this consumption decreases with time. When an adult feeds on third instar larvae or pupae, it destroys an average of 2.6 Diptera per day (Read, 1962) (Table 1.3). Fuldner (1960) stated that the fluid of the Diptera larva or egg attracts other predators because when one A. bilineata adult feeds on a larva other A. bilineata arrive rapidly.

There is no apparent courtship period in copulation. The male bends its abdomen over its head and its claspers and aedeagus are extruded (Figure 1.28). According to Colhoun (1953), the copulation lasts between 20 and 65 seconds. The pre-oviposition period can Vary from 36 to 96 hours (Wadsworth, 1915; Colhoun, 1953). This species is synovogenic as there is continuous production of eggs throughout the lifetime (Langlet, 1997). Adults A. bilineata can live an average of 49.7 days (40 to 72 days) (Read, 1962). In Quebec and Ontario there are two generations of A. bilineata per year. The first generation of adults is in midJune and the second in August or September (Nair & McEwen, 1975; Boivin et al., 1996).

A. bilineata is a solitary parasitoid but superparasitism is a common

occurrence. Up to five larvae can enter a host puparium (Wilde (1947) in Jones et al., 1993) but only one larva eventually survives (Colhoun, 1953; Read, 1962; Royer et a l , 1998a). In Delia floralis Zetter, the turnip maggot (Diptera: Anthomyiidae), multiparasitisrn by A.

bilineata and Trybliographa rapae

Westwood (Hymenoptera: Eucoilidae) is frequent (Brornand, 1980). According to Wishait and Monteith (1954), in al1 cases where both T. rapae and A. bilineala or A. bipustulata were in cornpetition, the T. rapae larva died. The A. bilineata larva

attacks and destroys both host and T. rapae larva. The fernale oviposits in the soi1 surrounding plants which are attacked &y

the dipteran host. The female is attracted by both decomposing cruciferous plants and plants attacked by Diptera hosts (Bromand, 1980). Colhoun (1953) states that th8 female oviposits approximately 15 eggs per day for an average of 700 eggs during her life. The female selects particular plants as suitable for

mating, foraging and oviposition sites (Tomlin et al., 1992). If the female is starved but has copulated, it will not oviposit because the avaries will not develop (Colhoun, 1953). In the laboratory, the female does not show preference for laying eggs on or near host puparia (Delia radicum) (Colhoun, 1953). Adults burrow galleries in the soi1 near infested plants to lay eggs near host puparia

B

(Wilde (1947) in Fuldner, 1960). The female oviposits eggs throughout her life but more than 90 per cent of eggs are laid between five and 50 days after emergence (Read, 1962). A. bilineata is a generalist that attacks several Anthomyiidae such as Delia

floralis Zetter (tumip maggot), D. florilega Zetter (potato maggot), D. platura Meigen (seedcorn maggot), D. antiqua Meigen (onion maggot) and D. radicum L. (cabbage maggot) with no apparent preference (Wishart, 1957; Fuidner, 1960; Moore & Legner, 1971; Klimaszewski, 1984; Jones et ab, 1993; Ahlstrom-Ollson, 1994; Jonasson, 1994). Other Anthomyiidae can be attacked such as Delia

planipalpus Stein, Pegomya hyoscyami Curtis (spinach leafminer) or Muscidae such as Musca domestica L. (housefly) and Calliphoridae, Call@hora

erythrocephala Meigen (Klimaszewski, 1984).

The ellipsoid egg is milky white at the beginning of its developrnent and its chorion is smooth. The egg varies between 0.38 to 0.50 mm in length and 0.32 to 0.37 mm in width (Wadsworth, 1915; Colhoun, 1953: Fuldner, 1960) (Table 1.4).

Twenty houn before hatching (at 23.a°C) it is possible to see through the chorion, the brown mandibles, black eye spots, antennae, legs of the larva and four chitineous dorsal protuberance (Colhoun, 1953; Fuldner, 1960). At this time the chorion turns yellow (Figure 1.3A) and the larva is curled along the longitudinal axis of the egg. Hatching occurs three to 19 days after oviposition, depending on temperature (Wadsworth, 1915; Colhoun, 1953; Fuldner, 1960).

The chorion is broken by the pressure of the head and by a twisting movement, the larva soon frees itself from the chorion. Hatching takes place in five to ten seconds (Colhoun, 1953).

2.4.3 First instar lama

The first instar larva is campodeiform and as such has functional legs. The size of the larva varies between 1.25 to 1.62 mm in length and 0.12 to 0.25 mm in width (Wadsworth, 1915: Colhoun, 1953: Fuldner, 1960). The larva is a very pale yellowish brown, with the intersegmental areas creamy white (Wadsworth, 1915) (Figure 1.38). These intersegmental areas are extensible (Fuldner, 1960). The head capsule, mandibles, legs and anal region are darker than the other regions of the body. The head of the larva is flat, has many sensorial bristles and possesses hard mandibles (Fuldner, 1960). The eye spots measure 0.015 mm in diameter and are conspicuous on each side of the head (Wadsworth, 1915). Each antenna has three well-developed segments. The larval abdomen has 10 segments and the last two are more sclerotized. The eighth segment bears pseudocerci that are used like tactile organs. The last segment has a pygopod that it used for locomotion and to anchor the larva to the host pupa (Fuldner, 1960). The respiratory system is well developed. There is a single pair of thoracic spiracles and one pair of spiracles on each of the first eight abdominal segments. At the end of the first instar, after feeding, the larva has increased its size to 2.2 to 2.5 mm in length and 0.37 mm in width (Colhoun, 1953: Fuldner, 1960). Upon emergence, the first instar larva (between one to three days old) searches for the host pupae. When it finds one, it drills a small hole in the pupariurn and enters (Reader & Jones, 1990) (Figure 1.4). When only one lawa attacks the host, the entrance hole is more frequently on the donum of the puparium (55%) than laterally (25%) or ventrally (20%) (Royer et a/., 1998b). When there are more than one larva, the hole can be on the ventrum of the puparium (Colhoun, 1953). The size of this hole is 0.08 to 0.17 mm in length and 0.015 in width (Wadsworth, 1915; Royer et al., 1998b). The process of drilting the hole takes from 12 to 36 hours (Colhoun, 1953; Fuldner, 1960). During its

exploration of the pupae, the first instar larva may search the external surface of the puparium and determine zones with fewer or lower transverse ridges (Royer

et al. 1998b). The lawa orients its mandibles parallel to the ridges and minimizes the number of ridges encountered (Royer et al. 1998b). Once it has entered, the

larva is very active and is attached to the puparium with its pygopods. The first instar larval stadium lasts five to eight days in the presence of hosts (Wadsworth, 1915; Bromand, 1980; Royer et al., lW8a). The larva overwinters as a diapausing first instar inside the puparium of its host (Colhoun, 1953; Bromand, 1980; Whistlecraft et al., 1985) which overwinters in diapause as a pupa. The emergence of the first generation adults is not synchronized with host emergence (Nair & McEwen, 1975; Whistlecraft et al., 1985) but rather with the presence of host pupae. Overwintered A. bilineata adults emerge no later than 2 weeks after the host adults had emerged (Nair & McEwen, 1975). At emergence, the larva has a fixed quantity of nutrients in the form of fat globules. After twelve hours several globules have disappeared (Fuldner, 1960) and after six to eight days without food, fifty percent of the larvae are dead (Colhoun 1953; Royer et al., 1998a). A. bilineata is an ectoparasitoid feeding on the host pupa and ingesting haernolymph by small punctures on the vertex of the head of the pupa. After entering the puparium, A. bilineata closes the hole, between two feeding periods, with excrement and the contents of malphigian tubules (Fuldner, 1960; Bromand, 1980). Before the hole is completely filled or if it is irnperfectly sealed, it is possible for nematodes or spores of fungus

(Fusariumsp.) to enter the host puparium. If this occurs, the first instar larva of A. bilineata is killed and the host pupa destroyed (Wadsworth, 1915; Bromand, 1980).

2.4.4 Second instar larva The larva, which was carnpodeiform in its first instar, turns into an eruciform larva (caterpillar form) in its second instar. This change in form indicates hypermetamorphism (Wadsworth, 1915: Colhoun, 1953). At the beginning of its second instar, the larva measures 2.8 mm in length (Colhoun, 1953; Fuldner, 1960). All characteristics of the first instar are lost; the legs are rudimentary and the bristles on the body are smaller than during the first instar. il is possible tu observe through the lama malpighian tubules that are white and opaque. The second instar larva is immobile and it rests on the thorax of the host pupa as does the fint instar (Colhoun, 1953). A parasitized puparium appears identical to an unparasitized one except that there are small brownish spots on puparium that appear with punctures made by the parasitoid. Ouring the second instar, the larva does not excrete except for occasional minute drops of a clear fluid substance that exits the anus. The second instar lasts five days (Colhoun, 1953). At the end of this stage, the larva rneasures 3.60 to 3.69 mm in length (Colhoun, 1953; Fuldner, 1960). 2.4.5 Third instar larva This instar is eruciform but the larva is more sclerotized than the second instar. The site ranges between 5.0 to 7.6 mm in length and 1.64 to 2.00 mm in width (Wadsworth, 1915; Colhoun, 1953; Fuldner, 1960). The respiratory systems of the second and the third instar are similar to the first instar. The feeding behavior of the third instar is very similar to that of the second. However it feeds more voraciously, beginning with the host head, then the thorax and finally the abdomen (Colhoun, 1953). The third instar lawa is U-shaped and its head now points toward the caudal end of the puparium. The head and thorax

of the larva continue to move in this direction until the body is straight. When the host has been completely eaten, except for the cuticle, the larva moves until its head is in the cephalic end of the puparium (Colhoun, 1953). The third instar has

a duration of six days (Colhoun, 1953). Wadsworth (1915) hypothesized that the lawa is then very active because the excreted substance is soon plastered over the inner surface of the puparium. The puparium becomes opaque, making observation of larvae difficult. This excretion phase has a duration of 36 hours

and, after two to t h e days of quiescence, the pupa starts to form (Coihoun, 1953; Fuldner, 1960).

2.4.6 Pupa The

pupa measures between 4.25

and 4.66

mm in length

(Wadsworth,1915; Colhoun, 1953). The host pupa is completely consumed by the larva and the pupa fills the puparium. In the beginning of this stage the pupa is white although towards the end it is black (Figure 1.5). The pupal stage has a duration of 14 days (Colhoun, 1953; Bromand 1980). The size of the host puparia determines the size of the A. bilineata adult

(Bromand, 1980). The adult emerges through a ventro-cephalic hole in the puparium made with its mandibles (Colhoun, 1953; Fuldner, 1960).

2.5 Geographical distribution A. bilineata is found throughout holarctic region (35O - 60" N) (Jonasson et

al., 1995; Langlet, 1997). According to Horion in 1967 (in Klimaszewski, 1984) it is assumed that A. bilineata was introduced to North Arnerica from Europe. A. bilineata ranges from British Columbia to Newfoundland in Canada and, to the south, to Oregon, Illinois and Massachusetts in United States (Klirnaszewski, 1984).

3. Delia radicum L. (Diptera: Ant homyiidae) Bouche has first described the cabbage maggot in 1833 as Anthomyia

brassicae (Coaker & Finch, 1971). The synonymy of this species is presented in table 1.5. The cabbage maggot is an important pest of cruciferous crops in Canada (cabbage, turnip, rutabaga, cauliflower, Brussels sprouts...) and it is one of the hosts of Aleochara bilineata,

3.1 Morphology

The cabbage maggot is sirnilar to the housefly, but smaller and more slender. The cabbage maggot adult is gray and is about 6 mm long (Smith, 1927) (Figure 1.6). The sexes can be distinguished by the fact that the male eyes are holoptic while the eyes of the female are dichoptic. The male has a hind femur which is very hairy on the basal half of the anterior surface. The female has a middle femur with strong anteroventral bristles near its base. The front femur has three to six small, erect bristles on its anterior surface and the front tibia has two posterior bristles (Brooks, 1951). 3.1.2 Egg

The egg of D. radicum is cylindrical, white and with a length ranging from 0.93 mm to 1.02 mm and is 0.3 mm wide at its median part (Figure 1.7) (Smith, 1927; Coaker & Finch, 1971; Neveu et ab, 1997). The chorion is sculptured into

longitudinal ridges and its convex side shows a longitudinal strip. Its anterior pole has a depression where micropyles are present. Its posterior pole is rounded and has several aeropytes (Neveu et al., 1997).

The cabbage maggot larva has three instars. The first instar larva has a cephalopharyngeal skeleton consisting of one rnedian hook with a paired plate on each side (Brooks, 1951). The fint instar larva measures about 1 mm in length (Smith, 1927) and has only posterior spiracles. The second and third instars also have anterior spiracles. The second instar larva (2 to 4 mm in length (Smith, 1927)) has posterior spiracies with two siits contrary to the third instar which has

three slits. Whereas the rnouth hooks of second instar larvae have two teeth on

their ventral surfaces, those of the third instar are smooth (Coaker & Finch, 1971). The third instar varies from 2 to 8 mm in length and frorn 1 to 2 mm in diameter (Smith, 1927) (Figure 1.8A). 3.1.4 Puparium The puparhm is milky white at the beginning of the pupal stage and

becomes reddish-brown and black toward the end, just before emergence. Its form is sub-elliptical with smoothly rounded sides. According to Smith (1927), the average puparium measures 6 to 7 mm long by 3 mm wide at the center (Figure 1.8B). The external surface of the puparium is characterized by transverse ridges

(Royer et ab, 1998b). According to Fraenkel & Bhaskaran (1973), these ridges appear during the formation of the puparium when a longitudinal muscular contraction shortens the length of the larva by one quarter.

The number of generations of D. radicum varies according to the region. There are one to three generations in North Arnerica (Turnock & Boivin, 1997). In Canada, there is one complete generation with a partial second in Newfoundland however, in southwestern Ontario and southern British Columbia, there are three generations (Nair & McEwen, 1975; MAPAQ, 1987; Turnock & Boivin, 1997). In Quebec, there are two to three generations each year (Chagnon & Payette, 1990; Turnock & Boivin, 1997). In southwestern Quebec, the first generation adults oviposit from the end of May until the end of June, (MAPAQ, 1987; Richard & Boivin, 1994). The second generation oviposits in mid-July. Generally, after a pre-oviposition period of about six to eight days (Coaker & Finch, 1971), the female oviposits on or just below the soi1 surface close to the main stem of the cruciferous plants. Young plants are preferred oviposition sites for cabbage maggot fernales. According to Finch (1974), under laboratory conditions the female oviposits 299 I 48 eggs in her life. The female has a oviposition cycle of 40 to 50 eggs, after which it has to feed. Eggs hatch within a week in the field (the egg developmental time depends on the temperature, and varies between two and fourteen days (Coaker & Finch, 1971)) and the first instar larva descends into the soi1 and feeds on the secondary roots of the cruciferous plant. After three to four weeks of larval feeding, the third-instar larva exits the root and pupates in the soi1 (Read, 1973). However, when the soi1 is very dry, the third instar larva can pupate in the root (Read, 1973). Cool and moist temperatures increase the survival of the larva and it is under these conditions that the highest losses are experienced by growers (Richard & Boivin, 1994). After two weeks of pupation, the adults emerge and live from two to five weeks (Smith, 1927).

3.3 Geographicai distribution The cabbage maggot is native of Palaearctic Region, ranging from the Atlantic to the Pacific Oceans and from Rabat, Morocco (38O02'N) to Murrnansk, Russia (68'59'N) (Turnock & Boivin, 1997; Turnock et al., 1998). According to Coaker and Finch (1971), the cabbage maggot is restricted to the temperate

-

zone of the holarctic region (35" 60° N). It was introduced in North America from Europe before 1856 (Turnock & Boivin, 1997; Turnock et ai., 1998).

3.4 Control In vegetable crops in Canada (1990), losses amount to 15.5% by diseases, 12.5O/0 by insects and 10.5% by weed. The production losses can be due to several types of pathogenic agents and pests such as bacteria, fungus, nematodes, insects, acarids, spiders, slugs, snails, weeds, parasitic plants.. . (Richard & Boivin, 1994). The cabbage maggot is an important pest of all cruciferous crops such as rutabaga, turnip, cabbage and cauliflower but also of radish, broccoli and Brussels sprouts. There are several methods to control the cabbage maggot population.

3.4.1 Cultural control

Several cultural methods are used for cabbage maggot control. It is recommended to delay planting until the beginning of July to prevent serious damage. However, these late plantings should not be in proximity to early cruciferous crops with high cabbage maggot populations (Read, 1973). Crop rotation and destruction of infested plants are also used.

3.4.2 Chemical control

Each year in Quebec, 11 840 kg of insecticides are used against the cabbage maggot, which represents 9% of al1 insecticides used in Quebec (Chagnon & Payette, 1990). Adults can be deterred from ovipositing around host plants by treating the roots of the plant or the soi1 around them with ashes, lime sulfur or other similar noxious substances. Although frequent treatrnents are necessary and this technique is not feasible on a large scale (Coaker & Finch, 1971). Two types of treatments are recommended in Quebec against the cabbage maggot (MAPAQ, 1987). The first is the treatment of transplantation

water with GUTHION 50-W. The second treatment is after transplantation. This is done by applying 3.75 liters in 1000 liters of water of BIRLANE 400-E or 2.404.80 liters in 1000 liters of water of LORSBAN 4-E. However, both these treatments c m darnage plant foliage. Moreover, these insecticides cause a reduction in the number of predatory beetles (Wright et a/., 1960). 3.4.3 Biological control A variety of organisms have been used against the cabbage maggot.

These include fungi (Empusa muscae Cohn kills the adults and Strongwe//sea

castrans Batko sterilizes the adults), nematodes (Steinemema feltiae), predators and parasitoids (Hugues & Salter, 1959; Wright et al., 1960; Coaker & Finch, 1971; Nair & McEwen, 1975; Finch, 1989; Chagnon & Payette, 1990). Some organisms have also been used to diminish the oviposition of the cabbage maggot like the garden-pebble moth, Evergestis forficalis L. (Lepidoptera: Pyralidae) whose laivae have sinapic acid in their frass. This acid deters cabbage maggot oviposition on othennrise acceptable plants (Finch, 1989).

The immature stages of the cabbage maggot are preyed upon by many arthropods. The eggs are food for trombidid mites, ants, carabid and staphylinid beetles. The larvae are food for ants, beetles and other anthomyiid laivae. Finally, the adults are food for many predators although only a few cases have been reported (Coaker & Finch, 1971). There are four major predators, the first one being the carabid beetle, Bembidion /ampros Herbst (Coleoptera: Carabidae) and the second one Trechus

quadristriatus Schrank (Coleoptera: Staphylinidae) which feed on cabbage maggot eggs (Wright et

al., 1960; Coaker & Williams, 1963; Coaker

& Finch,

1971). In England, these two major predators are responsible for destroying more than 90% of the eggs laid (Hugues, 1959; Wright et al., 1960; Coaker & Williams, 1963). The third and fourth predators are Aleochara bilineata and A. bipustulata

which feed on cabbage maggot eggs and larvae.

Several parasitoids Hymenoptera attack the larval stages of the cabbage maggot but only kill after pupation. There are five species of braconids, three species of cynipids and four species of ichneumonids (Wishart et ab, 1957; Hugues & Salter, 1959; Coaker & Finch, 1971). In Quebec, two species of Hymenoptera are observed: Tryblographa rapae Westwood (Eucolidae) and Aphaerata pallipes Say (Braconidae) (Boivin et al., 1993). Most of the parasitism is due to staphylinids (Coleoptera) which attack the pupal stage (Nair & McEwen, 1993). Two species are known: Aleochara bilineata

and A. bipustulata, the latter being more abundant (Wishart, 1957). In 1990 at Ste-Clotilde in southwestern Quebec, in a sample of cabbage maggot pupae, 55% was parasitized by A. bilineata (Boivin et ab, 1993). Moreover, A. biîineata

can parasitize up to 95% of cabbage maggot pupae independent of the type of soi1 or plant species (Boivin et ab, 1993). Nair and McEwen (1975) consider pupal parasitism as a stabilizing factor. In 1987 and 1988 in London (Ontario) an experiment was performed with rnarked A. bilineata in urban gardens. Only 3% of

A. bilineata were recaptured and population in gardens was not increased. Moreover, the adults were capable of flying at least 5 km under urban conditions to select particular gardens as suitable mating, foraging and oviposition sites (Tomlin et al., 1992).

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O

Figure 1.1: A- Aleochara bilineata and 6- A. bipustulata showing red spots on its elytra (Taken from Langlet, 1997) (Scale bar = 2 mm).

a

Figure 1.2: A- Aleochara bi/inea?afeeding on Delia radicum eggs (Taken from Langlet, 1997) (Scale bar = 2 mm). B- Mating behavior in Aleochara bilineata where

the male bends its abdomen over its head and its claspers are extruded (Taken from Langlet, 1997) (Scale bar = 2 mm).

Figure 1.3: A- Egg of Aleochara bilineata before hatching showing the visible eye spots and mandibles (Taken from Langlet, 1997) (Scale bar = 0.1 mm). B- First instar larva of Aleochara bilineata (Taken from Langlet, 1997) (Scale bar =

0.2 mm).

Figure 1.4: Pupa cf Delia radicum parasitized by Aleochara bilineata with the entry hole of the parasitoid larva and the first instar of A. bilineata visible through the puparium (Taken from Langlet, 1997) (Scale bar = 1 mm).

Figure 1.5: Pupae of Aleochara bilineata A- early stage and B- later stage (Taken from Langlet, 1997) (Scale bar = 1 mm).

Figure 1.6: A- Male and 8- female of Delia radicum (Taken from Langlet, 1997) (Scale bar = 2 mm).

Figure 1.7: Eggs of Delia radicum (Taken from Langlet, 1997) (Scale bar = 0.5 mm).

Figure 1.8: A- Larva of Delia radicum (Scale bar = 1 mm). 6- Pupae of Delia

radicum (Scale bar = 2 mm).

Table 1.l:Groups of animals where cannibalism behavior is known (Fox, 1975; Elgar & Crespi. 1992). Phylum Class Order Farnily

-

e~schelminthese mProtozoa *Mollusca eArthropods

OChordata

.Arachnida Chilopoda .Insecta

Coleoptera

akstrychidae Carabidae Chrysomelidae .Coccinellidae Cucujidae Gyrinidae mScolylidae Glphidae mstaphylinidae mTenebrionidae

O

Table 1.2: Synonymy of Aleochara bilineata Gyllenhal ( 1 81 0) and references.

Names

References

A. agilis Stephens (1832)

Klimaszewski (1984)

A. immaculata Stephens (1832)

Klimaszewski (1 984)

A. nitida Erichson ( 1 839)

Wadsworth (1915) & Klimaszewski (1984)

A. alpicola Heer (1 839)

Klimaszewski (1984)

A. nigricomis Gredler ( 1 866)

Klirnaszewski (1984)

A. anthomyiae Sprague (1870)

Wadsworth (1915) & Klimaszewski (1984)

Baryodma ontarionis Casey (19 16)

Colhoun (1953),Wishart (1 957) & Klimaszewski (1 984)

A. bimaculata Burks (1952)

W ishart (1957) & Klimaszewski (1 984)

Table 1.3 : Details consumptions of Delia radicurn preys by Aleochara bilineata.

Authors

Eggs and first instar tannie

fhird instar lawae

Read (1962)

952 (40 days x 23.8/day)

104 (40 days x 2.6lday)

1714 (72 days x 23.8/day)

187 (72 days x 2.6/day)

Bromand (1980)

2400

250

Langlet (1 997)

2526 (60 days)

----------------

Table 1.4: Length and width of Aleochara bilineata eggs according to authors. Authors

iength

Width

Age when measured

Wadswoith (1915)

0.38 mm

0.32 mm

Unknown

Colhoun (1953)

0.50 mm

0.37 mm

24 hours

Fuldner (1960)

0.45 A 0.03 mm

0.36

0.03 mm

48 hours

Table 1.5: Synonymy of Delia radicum L. according to regions and authors.

Names

Region

Reference

Anthomyiae brassicae Bouché ( 1 833)

First name

Coaker & Finch, 1971

Hylemya brassicae Bouch6

United States

Colhoun, 1953; Brooks, 1957; Read, 1962; Coaker &

Canada

Finch, 1971; Nair & McEwen, 1975; Finch, 1989.

France

Wadsworth, 1915; Smith, 1927; Coaker & Finch, 1971.

CoTthophila brassicae Bouche

Germany Russia

Phonbia barssicae Bouché

France

Coaker & Finch, 1971; Finch, 1989.

Germany Russia

Enoischia brassicae Bouché

Belgium

Coaker & Finch, 1971; Finch, 1974; Finch, 1989.

England Hylemyia brassicae Bouché

France Germany

Russia

Smith, 1927; Coaker & Finch, 1971; Finch, 1989.

CHAPTER II IMPACT OF FOOD AND HOST AVAlLABlLlTY ON SlZE AND

SURVIVAL

OF

EGGS

OF

ALEOCHARA

GYLLENHAL (COLEOPTERA: STAPHYLINIDAE)

BlLlNEATA

ABSTRACT Several factors can influence egg size in insects, including food and host availability or age and size of the ovipositing female. In Aleochara bilineata Gyllenhal (Coleoptera: Staphylinidae), egg size is highly variable and ranges from 0.010 mm3 to 0.042 mm3. We have tested the Ice Box Hypothesis that states that when resources are

scarce, a female should oviposit a larger proportion of trophic eggs to be eaten by emerging larvae. Our results indicate that when female A. bilineata were without food they oviposited significantly srnaller eggs but the presence or absence of potential hosts for the larvae did not influence egg size. However, when the proportion of hatched egg was compared between fed and unfed fernales, no significant difference was found. The Ice Box Hypothesis was not supported by these results. Egg size in A. bilineata appeared to be influenced positively by age of the ovipositing female and developmental stage of the egg.

Key words: Aleochara bilineata, egg size, Ice Box Hypothesis

Introduction When survivorship of offspring varies unpredictably, females rnay gain by increasing clutch size such that when resources are abundant, most offspring survive. However when resources are scarce, some eggs rnay seive as food for offspring (Ice Box Hypothesis) (Alexander, 1974; Elgar & Crespi, 1992). In Labidomera clivicollis Kirby (milkweed leaf beetle) (Coleoptera: Chrysomelidae), an average of 15-1796 of eggs are trophic and sterile. These eggs are homologous to fertile eggs, but they cannot develop into viable offspring. A certain amount of these sterile eggs are eaten by older lanrae from earlier hatching egg clutches (Dickinson, 1992; Elgar d Crespi; 1992). Many factors such as female size and age, food and, for parasitoid species, host quality can influence the size of the eggs laid (Karlsson, 1987; Berger, 1989; Fitt, 1990; Wallin et al., 1992; Fox, 1993a; Braby, 1994; Fox, 1994). For example, in Chilo parteilus Swinhoe (Lepidoptera: Pyralidae), large females lay larger eggs than small females (Berger, 1989) and in Pararge aegeria L. (Lepidoptera: Satyrinae), egg weight and oviposition rate decrease with female age (Karlsson, 1987). Aleochara bilineata Gyllenha1 (Coleoptera: Staphylinidae) adults are predators of dipteran eggs and l a m including the cabbage maggot, Delia radicum L. (Diptera: Anthomyiidae). The first instar larvae of A. bilineata are ectoparasitoids of the pupae of the same species (Fuldner, 1960; Brornand, 1980). After a pre-oviposition period of 36 to 96 houn, the females of A. bilineata oviposit approximately 15 eggs per day for an average of 700 eggs during their lifetime which ranges between 40 to 72 days (Wadsworth, 1915; Colhoun, 1953; Read, 1962). A. bilineata oviposits in the soi1 surrounding plants attacked by the cabbage maggot

(Bromand, 1980). The egg size varies between 0.38 to 0.45 mm in length and 0.32 to 0.36 mm in width (Wadsworth, 1915; Colhoun, 1953; Fuldner, 1960). At oviposition, the

egg is ellipsoid and white but, as it matures, its chorion turns yellow. Twenty-four hours before hatching, the rnandibles, eye spots, antennae and legs of the larva are visible

through the chorion (Colhoun, 1953). Hatching occurs between three days at 33OC to nineteen days at 10°C after oviposition (Wadsworth, 1915; Colhoun, 1953; Fuldner, 1960). After hatching, the campodeiform larva searches for its host, drills a small hole in

the puparium and enters (Reader & Jones, 1990). A. bilineata completes its three larval instars and pupates inside the puparium (Wadsworth, 1915; Colhoun, 1953; Fuldner, 1960; Bromand, 1980; Whistlecraft et al., 1985).

In this paper, the oviposition strategy of A. bilineata fernales in response to food and host (cabbage maggot) availability and the impact of female age and size on egg size and hatching rate have been studied in laboratory. The oviposition cycle and the pre-oviposition period of the female as well as developmental time of egg have been established.

Materials and methods General conditions

All rearing and experiments were done at 20°C, 60% RH and 16L:8N. A. bilineata was reared on the cabbage maggot. Cabbage rnaggot adults were fed with water, 10% honey solution and a mixture of 75:25 of brewer's yeast and soya flour. These were placed in presence of one-half rutabaga deposited in a dish covered with humidified sand (Royer et a1.,1998). These adults oviposited on the sand and the larvae entered the rutabaga to feed and pupate in the soil. For experiments, third instar larvae and pupae were used. 60th male and female A. bilineata, 24 hours-old, were sexed at mating and placed in a 5.0 cm dish containing a humidified piece of cotton. This experiment was done to determine the distribution of egg size and the effect of the presence of food and hosts on egg size and hatching rate. The adults A. bilineata were fed with third instar larvae of cabbage rnaggot every second day and were in piesence of eight host pupae

of the same species. During a period of 15 days, the eggs were collected daily with a bnish. With a binocular (IOOX), the eggs were measured in length and width. The eggs were individually placed in polyethylene capsules until hatching. These capsules were placed in 37 ml closed solo0 cups containing a humidified filter paper. The eggs are ellipsoid in form and their volume can be calculated as (Royer & McNeil, 1993):

Ovbosition strateav according to host and food availability In this expriment, the percentage of trophic eggs oviposited with or without food or pupae were measured. Eggs that did not hatch were considered as trophic eggs. The oviposition cycle, duration of pre-oviposition period of female and the distribution of egg sizes according to treatment were rneasured as well as developmental time of egg according to egg size. Finally, the relation between egg size and female age and size were established. To measure the effect of food and host on egg size and hatching rate, 40 couples were used: 10 were fed in the presence of hosts, 10 were fed without hosts, 10 were unfed with hosts and 10 were unfed without hosts. A correlation between weight of female and male and egg size were calculated. The adults were frozen and the width and length of their pronotum measured. Royer (personal communication) has establish a correlation between the weight (mg) of A. bilineata adults and the surface of their pronotum (mm2):

f(x) = 1.7975 * 10" x + 3.41 18 ' 1O-'; F12= 0.77 for female and f(x) = 1.2843 1O-' x + 4.491 1 '10"; FI2=0.67for male where x is the weight of A. bilineata adults.

A Kruskal-Wallis test has been used to compare hatching rate according to treatments. Normality has been verified by Kolmogorov-Smirnov tests on: the impact of food and host availability on egg size, oviposition cycle, duration of pre-oviposition period and female weight. The data were analyzed by ANOVA followed by Fisher's

PLSD tests. The relations between egg size and adult weight, female age and developrnental time of egg were established by linear regression. An unpaired Student-t test has been used to compare volume of hatched and sterile eggs.

Presence of trophic eggZ No significant difference in hatching rates was found between treatments: (mean î

confidence interval of proportion) 86.34 I30.31 % for fed couples with hosts, 78.07

I

33.72 % for fed couples without hosts, 71.19 t 41 2 2 O h for unfed couples with hosts. No eggs were laid by unfed couples without hosts (H=5.32; df=2; 0.10 < P < 0.05). However, the eggs that did not hatch were smaller (0.018 î 0.003 mm3) than viable eggs (0.019 I 0.004 mm3) (k3.827; df=l526; P=0.0001) but this difference was very small.

Influence of host and food availability There was a significant difference in egg size according to treatments (F=7.8020; df=2,1370; P=0.0004). Eggs laid by fed couples with (mean f SD: 0.01 9 k 0.004 mm3)

or without (0.019 k 0.004 mm3) hosts were significantly larger than those laid by unfed

+

couples with hosts (0.017 0.004 mm3) (Figure 2.1 ).

a

The age and weight of female can also affect the egg size laid. There was a weak positive correlation between egg size and fernale age (~=0.018+1.07~xl U ~ X ;~~=0.009; P=0.0004) and between egg size and weight of female (Y=0.17+0.001X; ~~=0.004; P=0.0181). There was no significant difference in female weight between treatments (F=0.269; df=2,17; P=0.7675). The average female weights were: fed with hosts = 1.913 î

0.436 mg, fed without hosts = 1.839

* 0.226 mg and unfed with hosts = 1.972 I0.376

mg. Moreover, larger males did not stimulate production of larger eggs by females as there was no correlation between male weight (1.90

*

0.39 mg) and egg size

(~=0.019+3.672~1 O"X; R*=I .39 x 1O"; P=O.8949). Fed females with hosts laid significantly more eggs per day (8.56 & 4.85 eggs) than fed females without hosts (5.91 k 3.59 eggs) and significantly more than unfed females with hosts (0.67

+ 1.31 eggs) (F=23.313; df=3,48; Pc0.0001) (Figure 2.2). In al1

treatments, the average developmental time of egg was 6.0 I 0.5 days at 20°C, which corresponds to reports in the literature (Wadsworth, 1915; Colhoun, 1953; Fuldner, 1960). Moreover, there was a correlation between egg size and developmental time (Y=O.O26+O.OOl X; FI2=0.024; P 1 population increase) (Abercornbrie et a/., 1980). Fitness is a short-term measure of reproductive success and general adaptedness (de Jong, 1994). Several parameters contribute to fitness including: viability, fecundity, egg load at ernergence, egg size, travel speed and searching efficiency (de Jong, 1994; Visser, 1994). While most studies examine the fitness of adults, the fitness of larvae can be measured with the same parameters. Brady (1994) has measured three offspring fitness parameters in butterflies of the genus Mycalesis; larval survival, larval developmental time and pupal weight in relation to egg size. There was a correlation between egg weight and larval fitness. Larvae from heavier eggs had a higher survival, developed faster and produced larger pupae than larvae fmrn lighter eggs. Çuch a relationship iç not always present, in

Paraarge aegeria L. (Lepidoptera: Satyrinae) there was no correlation between egg weight and egg survival, larval survival, larval developmental time and pupal weight (Wiklund & Persson, 1983). However, variation in offspring size or weight may influence survival and thus affect the reproductive success of the female (Braby, 1994).

Aleochafa bilineata Gyllenhal (Coleoptera: Staphylinidae) adults are predators of eggs and larvae of dipteran species and its first instar larvae are ectoparasitoids of dipteran pupae (Reader & Jones, 1990). A. bilineata females oviposit in the soi1 near plants infested by the dipteran host (Colhoun, 1953; Read, 1962; Bromand, 1980). Hatching occurs three to 19 days after oviposition, depending on the temperature (Wadsworth, 1915; Colhoun, 1953; Fuldner, 1960). At emergence, the larva varies in size between 1.25 to 1.62 mm in length and

0.12 to 0.25 mm in width (Wadsworth, 1915; Colhoun, 1953; Fuldner, 1960) and it has a fixed quantity of nutrients in the fom of fat globules that start diîappearing after twelve

hours (Fuldner, 1960). After six to eight days without food, 50% of larvae are dead (Colhoun, 1953; Royer et al., 1998). A. bilineata is a solitary parasitoid even if superparasitisrn is common but then only one larva eventually survives. No masure of the fitness of Aleochara bilineata larvae is available at the moment. In fernale parasitoids, there are four principal constraints which affect their fitness: longevity (time-limited), fecundity (egg-limited, where pro-ovogenic females have a fixed number of eggs and synovogenic fernaies produce eggs during all their lifetime), host-

finding ability (optimal foraging, to maxirnize the research) and environmental conditions (temperature, humidity) (Driessen & Hemerik, 1992; Visser, 1994). In parasitoid species where the larvae search for a host, many constraints affect their fitness. The first is longevity because if the larva does not find a host, it cannot develop. Second, the hostfinding ability of the larva can be affected by many factors. In A. bilineata larvae, soi1 humidity is an important factor, as humidity can soften the host puparium and facilitate entrance for the larva (Wadsworth, 1915; Fuldner, 1960). The third factor is the

O

developmental stage of the host pupa. A. bilineata first instar larva enters the host puparium after the last molt of the host pupa. It does this because, at this time, there is a space between the pupa and the puparium (Fuldner, 1960). This pupa host is at the stade phanerocephalic (Fraenkel & Bhaskaran, 1973). The fourth factor is the level of superparasitism which is common and inevitably results in lawal mortality. This occurs since A. bilineata is a solitary parasitoid (Colhoun, 1953; Fuldner, 1960; Read, 1962). After a larva has found a host, it drills a small hole in the puparium and entes. The second and third instan are erucifon (no functional legs), and A. bilineata pupates in the host puparium. We observed an important variability in A. bilineata egg size before and after swelling; before: 0.013 to 0.026 mm3 and after 0.021 to 0.043 mm3 (Gauvin, unpublished data). We assume that lawae hatching from small eggs are smaller than those hatching from large eggs as for Callosobruchus maculatus F. (Coleoptera) or the genus Mycalesis (Lepidoptera) where egg size is positively correlated with laival size

(Fox, 1993a; Fox, 1993b; Braby, 1994).

In this paper, the impact of size on the fitness of A. bilineata larvae has been evaluated with three parameters: longevity, walking rate and host searching capacity.

Materials and methods General conditions

All experiments and rearing (parasitoids and hosts) were made at 20°C, 60% relative humidity and a photoperiod of 16L:8N. A. bilineata has been reared on the cabbage maggot, Delia radicum L. (Oiptera:

Anthornyiidae). Adults of cabbage maggot were fed with water, 10% honey solution and

a mixture of 75:25 of brewets yeast and soya Ilour. They were placed in the presence of one-half rutabaga deposited in a dish containing damp sand (Royer et al., 1998). Twenty adults of A. bilineata (sex ratio 1:l) were placed in a dish containing a dampened piece of cotton for oviposition. Five oviposition dishes were used. They were fed with third instar larvae and host pupae of cabbage rnaggot were present. The eggs were collected with a brush and placed individually in polyethylene capsules until hatching. The capsules were placed in closed 37 ml SOLO@cups containing moist filter paper. Each hour, hatching was verified to obtain larvae 30

* 30 minutes-old for al1

experiments. The larvae were weighed with a Cahn 29 scale capable of weighing up to 0.0001 mg and classified as small or large larvae. The average weight of 185 larvae was 0.027 t 0.002 mg. We used this value to classify our larvae. Larvae weighing less than 0.025 mg were classified as small l a m e while large larvae were those weighing more than 0.029 mg. The small and large larvae represented respectively 32.4% and 41. l % of al1 larvae weighed (Figure 4.1 ). For these experiments, larvae between 10.025; 0.029[ were not considered.

To evaluate the effect of larval size on longevity, 30 srnall and 30 large larvae of 30 t 30 minutes were used. The day and hour of emergence of each larva was noted to

calculate its longevity. The larvae had no access to food. They were placed individually in polyethylene capsules within a closed 37 ml SOLO' cup and covered with a piece of moist filter paper. Twice a day, at 9:00 and 16:00, the larvae were checked until found dead (complete absence of movement by the larva) and the day and hour of death were noted, Walkincl rate

An image analysis system has been developed to measure the mean diameten

of air bubbles in a water tank (Vigneault et al., 1992; Orsat et ab, 1993). This technique has been modified and adapted to study insect behavior (Vigneault et al., 1996;

a

Vigneault et al., 1997). The system was comprised of background light, an acrylic plate,

an incubator at 20°C, monochrome carnera (Panasonic) with a lens of 16 mm, video VHS, two computer monitors, one TV monitor and an IBM-AT compatible personal computer (Figure 4.2). Each larva (20 small and 20 large) was placed individually in a 5.0 cm diameter arena and observed for 300 seconds. This system analyzes the path of larvae. The following parameters were measured: mean walking rate, number of stops, duration of stop and real walking rate (mean walking rate minus lime stopped).

Searchina cawcity A phanerocephalic pupa (average of 7.0 mm) of the cabbage maggot was placed

in the center of a 37 ml SOLO@cup on 1 ml of sand moistened with 0.3 ml of distilled water. The pupa was covered with 2 ml of sand moistened with 0.3 ml of distilled water.

Each A. bilineata larva was individually placed on a 25 mm2 diameter filter paper on the

surface of the sand at the center of the cup. The cup was then closed and placed in an incubator for 48 hours. After that period, the pupa was extracted from the sand. It was then examined by transmitted light using a transillumination unit for brightfieldidarkfield (Royer et al., 1998). The position of A. bilineata first instar laivae was noted: larva did not find host pupa, larva in contact with host but not entered and larva entered the puparium of the host. This experiment was replicated for 20 small and 20 large A. bilineata l awae.

Statistics Unpaired Student tests were used for longevity, mean walking rate, number of stops, duration of stops and real walking rate according to larval categories (small or large). A G-test was used to compare the A. bilineata larvae did not find host, on the host and inside the host.

Results and discussion Lonaevitv Large larvae lived longer (mean I SD; 160.64 î 41 .O4 hours) than small larvae (132.89

I61.85

hours) (t= 2.242; df= 58; P= 0.0282). It is the first instar larva that

searches for the host, increased longevity is advantageous since the larvae do not necessarily emerge near the host. The increase in longevity of the larva increases the possibilities of finding and parasitizing a host. A female parasitoid that has short longevity and lays many eggs may have a higher fitness than a parasitoid with high longevity but that lays few eggs. However, this may be the opposite in a different environment. One important characteristic of the environment for parasitoid is the abundance of hosts because longevity increases in importance with decreasing encounter rate of hosts (Visser, 1994). The large larvae had 17.27% more time than small larvae to find and parasitize a host. Therefore, we can conclude that they had a better fitness. In Pararge aegeria L. (Lepidoptera) fernales lay their eggs on the host for larval

feeding immediately after the larme have hatched. The capacity to withstand starving conditions is not important (Wiklund & Persson, 1983). This capacity becomes especially important when the females lay eggs quite a distance from the larval host plants as with Oenis jufta and Erebia iigea both Lepidoptera (Wiklund & Persson, 1983). In the genera

Chrysopa and Chrysoperla (Neuroptera), the larva must search and capture prey that may be distant from the oviposition site. The egg size and the sutvival of larvae during host searching increase with increasing materna1 allocation of resources by the female (Tauber et al., 1990). A. bilineata larva is similar to these cases because the fernale oviposits her eggs near an infested plant. However, this is not necessarily near host pupae and the larva may have to search for a host (Colhoun, 1953; Read, 1962, Bromand, 1980). Therefore, the capacity to withstand starving conditions of first instar lama of A. bilineata is important and this capacity c m be measured by the larval kngevity. In A. bilineata larva there is a fixed quantity of nutrient in the form of fat

globules and these have already disappeared after twelve hours (Fuldner, 1960). These fat globules probably allow A. bilnieata larvae to withstand starving conditions. This may be due to the fact that larger larvae have a relatively greater food reserve than smaller larvae.

Walkina rate Large larvae had a higher mean walking rate (0.406

t

0.134 mmh) than small

larvae (0.264 I0.132 mmts) (t=3.368; df=38; P=0.0017), stopped less often (26.1 I23.2 stops) than small larvae (40.85 t 29.61 stops) (t=-1.754; df-38; P=0.0875) and for a shorter time (23.53

I

20.98 s) than small larvae (60.40 i 54.03

s) (t=-2.691; df=38;

P=0.0105). As a result, large larvae had a higher real walking rate (0.441 I0.137 mrn/s) than small larvae (0.318

* 0.120 mmls) (t=3.023; df=38;

P=0.0045). Therefore large

larvae had an increased chance to find a host as compared to small larvae. This is due to the fact that they walked 27.89% (real walking rate) faster and covered more ground.

a

For a larval parasitoid, the searching capacity is especially important when its longevity is short. Royer et a/. (1998) mentioned that, after six to eight days, 50% larvae of starved

A. bilineata are dead. The larva reduced his chance to parasitize a host, if it takes more than 6 to 8 days to find a host due to factors such as walking slowly or stopping too often or for too long (because it has not enough energy). The capacity to walk rapidly increases the probability of parasitizing a host which has not already parasitized. This factor is important since A. bilineata is a solitary parasitoid, and only one larva completes its development in the host. In addition, small larvae have more chance of being attacked by generalist predaton because their stopped time was longer as compared to large larvae. In some species, the ability of young hatchlings to successfully disperse to a hostplant is correlated with egg size (Braby, 1994). In Lymantna dispar L. (Lepidoptera), large larvae have greater resources and disperse quicker than smaller larvae (Berger, 1989). In Lepidoptera, fernales oviposit their eggs on the host-plant. Therefore, the efficiency of movement and travel speed are not important. However, this factor

becomes important for an insect where the female oviposits her eggs quite a distance from the larval envimnment. In the genus Chrysopa (Neuroptera), the egg size is positively correlated with tibial length. The authors suggest that tibial length is related to the speed and efficiency of movement (Tauber et al., 1990). The speed and efficiency of movement are especially important for A. bilineata larva that searches and captures its PreY

The percentage of large larvae in each category (host not found, on and inside

host) was significantly different from small larvae (G-6.61 9; P=0.0365) (Figure 4.3). Large lawae are 1.6 more efficient at finding (on host: 20% and inside host: 70%) hosts as compared to srnall larvae (on host: 15% and inside host: 40%).

Visser (1994) has evatuated the searching efficiency (optimal foraging) of Aphaereta minuta Nees (Hymenoptera) female for discovering patches. This is measured as the total time spent on patches in a female lifetime. Visser states that a number of factors influence the total time spent on patches in the lifetime of a female: its longevity, its ability to locate patches and its travel speed. In A. minuta the longevity of a female is positively correlated with its size (no correlation with other factors). In A. bilineata longevity, travel speed and the ability to locate patches (searching capacity) are

positively correlated with larval size. All three factors contribute to an increased probability of successful host finding, therefore increasing fitness. The large laivae lived 17.27% longer, walked 27,89% faster and found hosts 1.6 more frequently than small

lanrae.

Im~actof size of fitness There is a cost to producing large larvae as the female has to allocate a larger quantity of resources in cornparison to smaller eggs. However, this cost is compensated by a high fitness for large larvae. If the fitness increases with larval size (and egg size),

O

we may ask why females lay small eggs. At the lawal level, the fitness is not necessarily the same as at the parental level. When females have fewer resources to invest in their eggs, it may be beneficial to invest scarce resources in numerous small eggs (Braby, 1994). When females oviposit their eggs they do not always have access to suitable

dipteran food (eggs or larvae) which allows for the production of larger eggs. However they may be in the presence of dipteran host pupae, which are suitable hosts for first instar larvae hatching out of the eggs. In the case of high pupa abundance the fitness of females will be increased with the number of eggs oviposited. This occun even if these eggs have a small amount of resources. It is possible that there are disadvantages for large larvae in particular conditions. At times, this pressure may favor the production of many small offspring by the female. In Tyfia jacobaeae L. (Lepidoptera), low temperatures (15OC) in egg size is positively correlated with hatching success. However at high temperature (22OC), there is disadvantage for large eggs by decreasing hatching success (Braby, 1994). When the species Mycalesis are reared on the softer nitrogen-rich host-plant, the advantage to larger larvae diminishes (Braby, 1994). As with these species, the large larvae of A.

bilineata can be disadvantaged in certain conditions. A disadvantage for the large larva could be reduced mobility in the soil. The larval size can be negatively correlated with the mobility in certain soi1 conditions (for example, compressed soil) and the lawa cannot parasitize a host.

References Abercombie, M., C.J. Hickman & ML. Johnson. 1980. The Penguin dictionary of biology. 7e edition. Penguin reference. London. 323~.

Berger, A. 1989. Egg weight, batch size and fecundity of the spotted stalk borer, CMo partellus in relation to weight of females and time of oviposition. Entomol. Exp. & Appl. 50: 199-207. Braby, M.F. 1994. The significance of egg size variation in butterflies in relation to hostplant quality. Oikos 71:119-129.

Bromand, B. 1980. Investigations on the biological control of the cabbage rootfly (Hylemya brassicae) with Aleochara bilineafa. Bull. SROPMIPRS 3:49-62. Colhoun, E.H. 1953. Notes on the stages and the biology of Baryodma ontarionis Casey (Coleoptera: Staphylinidae), a parasite of the cabbage maggot, Hylemya

brassicae Bouche (Diptera: Anthomyiidae). Can. Entomol. 85:1-8.

de Jong, G. 1994. The fitness of fitness concepts and the description of natural selection. Quart. Rev, Biol. 69: 3-29.

Driessen, G. & L. Hemerik. 1992. The time and egg budget of Leptopilna clavipes, a parasitoid of larval Drosophila. Ecol. Entomol. 1 7: 17-27.

Fox, C.W. 1993a. Matemal and genetic influences on egg size and larval performance in a seed beetles (Callosobruchus maculafus): multigenerational transmission of

a materna1effect. Heredity 73509-517.

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Fox, C.W. 1993b. The influence of materna1 age and mating frequency on egg size and offspring performance in Callosobruchus maculatus (Coleoptera: Bruchidae). Oecologia 96: 139- 146.

Fox, C.W. 1994. The influence of egg size on offspring performance in the seed beetle, Callosobruchus maculatus. Oi kos 71:321-324. Fraenkel, Ga & GaBhaskaran. 1973. Pupariation and pupation in cyclorrhaphous flies (Diptera): terminology and interpretation. Ann. Entomol. Soc. Am. 66:418-422.

Fuldner, D. 1960. Beitrage zur morphologie und biologie von Aleochara bilineafa Gyll. und A. bipustulata L. (Coleoptera: Staphylinidae). [Traduction: Contribution a la morphologie et à la biologie de Aleochara bilineafa Gyll. et A. bipustulata L. (Coleoptera: Staphylinidae)]. 2. Morph. 0kol. Tiere. 48:s 12-386.

Orsat, Va, C. Vigneault, G.S.V. Raghavan. 1993. Air diffusers characterization using a digitized image analysis system. Am. Soc. Agr. Eng. 9:115-121.

Read, D.C. 1962. Notes on the life history of Aleochara bilineafa (Gyll.) (Coleoptera: Staphylinidae), and on its potential value as a control agent for the cabbage maggot, Hylemya brassicae (Bouche) (Diptera: Anthomyiidae). Can. Entomol. 94~417-424.

Reader, RH. & T.H. Jones. 1990. Interactions between an eucoilid (Hymenoptera) and

a staphylinid (Coleoptera) parasitoid of the cabbage root fly. Entornophaga 35~241-246.

Royer, L., S. Fournet, E. Brunel 8 Ga Boivin. 1998. Intra- and interspecific host discrimination by host-seeking larvae of Coleopteran parasitoids. Oecologia in press.

Tauber C.A., M.J. Tauber & MmJm Tauber. 1990. Egg size and taxon: their influence on survival and development of chrysopid hatchlings after food and water deprivation. Can. J. Zool. 69:2644-2650.

Vigneault, CD,B. Panneton & G.S.V. Raghavan. 1992. Real time image digitizing system for measurement of air bubbles. Can. Agr. Eng. 34:151-155.

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Visser, MD€.1994. The importance of being large: the relationship between size and fitness in females of the parasitoid Aphaereta minuta (Hymenoptera: Braconidae). J. Anim. Ecol. 63:963-978.

Wadsworth, J.T. 1915. The life-history of Aleochara bilineata, Gyll., a staphylinid parasite of Chofluphila brassicae, Bouch6. J. Econ. Biol. 10:l-27.

Wiklund, C. & A. Persson. 1983. Fecundity, and the relation of egg weight variation to offspring fitness in the speckled wood butterfly Pararge aegeria, or why don? butterfly fernales lay more egg? Oikos 40:53-63.

Figure 4.1 : Distribution of weight of 185 larvae of Aleochara bilineata 30 i 30 minutes after hatching.

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Figure 4.2: Schematic representation of the experimental setup.

Figure 4.3: Percentage of srnall and large Aleochara bilineata lame that did not find a host, found a host but did not penetrate and found a host and penetrate after a period of 48 hours.

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GENERAL CONCLUSION

The objectives of this research were; (1) to evaluate the impact of food and host availability along with age and weight of female on egg size of Aleochara bilheata; (2) to understand the developmental biology of hydropic eggs of A. bilineata; (3) to measure the impact of size on the fitness of A. bilineata first instar laivae. We have observed that the presence of food increased egg size and that females needed food to develop their ovaries and produce eggs. Moreover, oider fernales laid larger eggs than younger fernales. Under our experimental conditions. we observed a wide range of egg size (0.010 to 0.042 mm3). However, the factors studied (availability of food and host as well as female age and weight) accounted for a small, although significant, difference in average egg size (0.017 to 0.019 mm3). The wide range of egg size can be explained by the fact that, in our experiments, the age of the A. bilineata eggs was not constant when they were measured. Thirty hours after oviposition, these eggs began to absorb water and, as a result, swelled. This absorption continued up to 50 hours after oviposition, after which the egg volume remained stable until emergence. In transmission and

scanning electronic microscopy, we obseived that this swelling produced a splitting of the endochorion. However, hydropy did not explain cornpletely the variability in egg size. After swelling, a wide range in egg size (0.021 to 0.043

mm3) was still obseived. Differences in egg size are known to result in difference in larval size and consequently in larval fitness. When parameters related to larval fitness were measured, we showed that larger fint instar larvae of A. bilineata lived longer, walked faster and

displayed a better host searching capacity. These three parameters are very important for A. bilineata first instar larvae because they increase the probabilities to find and parasitize host.

The absorption of water by the egg is observed in several aquatic (e.g. Plecoptera, Hemiptera and Coleoptera) and terrestrial insects (e.g. Orthoptera, Hymenoptera and Coleoptera). In terrestrial insects, ovipositing hydropic eggs can be costly when no water is available because morlality rate will be higher since water absorption is necessary to cornplete egg development. In such species, females oviposit their eggs in situations where water is normally available or at least available at certain time (Hinton, 1981). In A. bilheata, female oviposits their eggs near the host pupae (the female makes galleries in the soil) in damaged cruciferous plant where water is present (Wilde (1947) in Fuldner, 1960; Bromand, 1980). This is similar to Ocypus olens Müller (Staphylinidae), whose females oviposit their hydropic eggs on soi1 surface where water is normally available as humidity or rain (Lincoln, 1961). In Coleoptera, two others families have hydropic eggs, the Scarabaeidae and Elateridae that both oviposit their eggs in plant tissues and in soi1 where water is available at certain time (Hinton, 1981; Paulian, 1988). By investing fewer resources (water) in each hydropic egg, a fernale can oviposit more eggs. lncreasing its progeny can be very important for a female parasitoid when it is the first instar larva that has to search and locate the host. Lawae that search for host are present in Lepidoptera (10 species), Neuroptera (50 species), Hymenoptera (500 species), Coleoptera (3 590 species) and Diptera (8 600 species) (Eggleton & Belshaw, 1992; Godfray, 1994). Because of the expected high mortality rate of these searching larvae either through predation, parasitism or simply lack of suitable hosts, most of the species where larvae searches for host have a high fecundity as in A. bilineata. Two scenarios can explain the presence of hydropic eggs in A. bilineata. The first one is that hydropic eggs were present in Staphylinidae before some species became parasitoids. The second one is that hydropic eggs appeared as a secondary character of the parasitoid mode of life. According to Eggleton & Belshaw (1992), there is only one acquisition of parasitism for the Staphylinidae

which includes 500 parasitoid species out of 30 000 species. We know that O.

olens, that is not a parasitoid, has hydropic eggs. This fact alone suggests that hydropic egg is an ancestral character present in both parasitoid and nonparasitoid Staphylinidae. However, a thorough research more specific on Staphylinidae eggs would be required to confirm this hypothesis. Several other aspects remain to be studied in A. bilineata reproduction biology. The effect of relative humidity on egg hatching rate could be studied along with oviposition site selection by females. The impact of soi1 conditions (texture, hurnidity) on laival mobility needs also to be studied to evaluate larval fitness. Finally, verifying the fitness of the larvae on a longer period of time (> 48 hours) would provide a better understanding of the respective fitness of large and small larvae.

O

References Bromand, B. 1980. Investigations on the biological control of the cabbage rootfly

(Hylemya brassicae) with Aleochara bilineata. Bull. SROPMIPRS 3:49-62. Eggleton, P. & R. Belshaw. 1992. lnsect parasitoids: an evolutionary overview. Phil. Trans. R. Soc. Lond. 337: 1-20.

Fuldner, D. 1960. Beitrage zur morphologie und biologie von Aleuchara bilineata Gyll. und A. bipustulata L. (Coleoptera: Staphylinidae). [Traduction: Contribution à la morphologie et à la biologie de Aleochara bilheata Gyll.

et A. bipustulala L. (Coleoptera: Staphylinidae)]. 2. Morph. 0kol. Tiere. 48:312-386.

Godfray, H.C.J. 1994. Parasitoid behavioral and evolutionary ecology. Princeton University Press, Princeton, New Jersey. 473p.

Hinton, HE. 1981. Biology of insect eggs. Pergamon Press. Oxford. 1125p. Lincoln, O.C.R. 1961. The oxygen and water requirements of the egg of Ocypus

olens Müller (Staphylinidae, Coleoptera). J. lnsect Physiol. 7:265-272.

Paulian, R. 1988. Biologie des Coleoptdres. Éditions Lechevalier. Paris. il 9 p.