OIE news. Causes of bee colony mortality

OIE news Causes of bee colony mortality Reza Shahrouzi International beekeeping consultant, The environment and agriculture depend on a wide variety ...
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OIE news Causes of bee colony mortality Reza Shahrouzi International beekeeping consultant,

The environment and agriculture depend on a wide variety of pollinating species, including 20,000 species of hymenoptera,

P.O. Box 34185-451, Qazvin-Iran.

the most important being the domestic honey bee (Apis mellifera).

E-mail: [email protected]

Worldwide, the annual value of this ecological service is estimated to be in excess of a hundred billion dollars. Since 1997, numerous eye-witness accounts and published articles have reported an apparent weakening and mortality of bee colonies in various countries around the world. The beekeeping profession estimates that national production of honey fell by 20 to 30% between 1997 and 2009. The depopulation observed in apiaries is sometimes severe, leading to a reduction in honey production in the same proportion as the reduction in the number of bees. The weakening that occurs at the end of the beekeeping year may also result in a higher frequency of mortalities in winter.

One can define six categories of causes of mortality of bee colonies: – bee diseases and parasites; – chemical products; – the environment; – beekeeping practices; – agricultural practices; – treatment of varroosis.

Bee diseases and parasites

mortality of bee colonies, some have been highlighted in the most recent

Like all living organisms, bees may be

The pathogens responsible for diseases

investigations into the phenomenon

exposed to a variety of chemical

and parasitic infestations are predators:

of weakening, collapse and mortality

substances potentially present in the

parasites, fungi, bacteria and viruses.

of bee colonies, either individually

environment. In crop producing areas,

or in association with others. This is

most of these chemical substances

pathogens of bees. This precise figure

the case with Varroa destructor,

come under the heading of

is based on numerous bibliographic

alone or in association with other

phytosanitary products or pesticides.

references, including recent studies on

biological pathogens (viruses;

A phytopharmaceutical product is any

the decline of bee populations. While all

Tropilaelaps mercedesae and

product that, through its mode of

of them have the potential to cause

Nosema ceranae).

action, is designed to protect a crop

To date, there are 29 known

Chemical products

2009 • 4


all the vital functions, such as enzymatic functions and reproduction. Pollen is notably involved in the development of the hypopharyngeal glands of young bees and their fat body. If the pollen intake is insufficient these glands do not develop correctly in nurse bees, whose production of royal jelly no longer allows normal development of the brood or adequate food for the queen (the protein supplied by hypopharyngeal secretions represents about 95% of the protein required for the development of a larva). Pollen is stored in cells in the form of bee bread, comparable to silage, and has a higher biological © LeConte Pollen-gathering bee on acacia

value than fresh pollen due to fermentation (through the action of

from a harmful organism and usually

thermoregulation, various tasks

three strains of Saccharomyces and a

has a specific action for a given type

involved in maintaining the hive such

strain of lactobacilli) (Pain & Maugenet,

of target. Such products include

as cleaning cells, feeding the brood,

1966). Since the protein content varies

fungicides, herbicides, insecticides,

foraging, etc. Carbohydrates are usually

according to the botanical source, the

nematocides, molluscicides,

stored in the body as fat. The sugars

required amount of pollen to supply

rodenticides and avicides. The

present in floral secretions (nectar) are

a given quality of protein can therefore

catalogue of phytosanitary products lists

metabolised by bees (glucose, fructose,

be 50% less if the protein level

some 450 active agents and some

trehalose, maltose), whereas those

increases from 20% to 30%. In a

5,000 corresponding commercial

present in the secretion (honeydew)

period of medium honey flow, this level

products (survey conducted by the

of certain insects are not (raffinose).

must be at least 25%, and exceeds

French association ACTA (Association

Thermoregulation is a very important

30% during periods of heavy honey

de coordination technique agricole).

requirement, in particular to maintain

flow (Kleinschmidt, 1986). The

a temperature of 34°C in the presence

balance between amino acids varies

of brood.

considerably according to the plant

The environment

source. Very little information is currently

The environment is frequently

swarm should not fall below 13°C. In

mentioned as a potential cause of

temperate regions, a bee colony’s sugar

available on the nutritional

mortality of bee colonies: two factors

consumption can range from 19 to

requirements of bees in terms of lipids

that have been incriminated are food

25 kg in winter and total around 80 kg

(fatty acids, sterols and phospholipids).

resources and climatic factors.

during a full year. Numerous factors

These requirements are provided for

affect the quantity and quality of pollen

by the consumption of pollen. Of the

and nectar gathering by an apiary.

lipids, sterols are involved in the

Food resources Carbohydrates are among the most


In winter, the temperature of the

Protein is provided by pollen.

production of the moulting hormone

important food constituents, covering

A sufficient intake is essential for a bee

(ecdysone) and are therefore

the energy requirements for

colony, to ensure growth and maintain


2009 • 4

OIE news same as those normally found during

queen can result in the death of the

do not appear to pose such serious

the brood period (1.5% CO2 and 35°C

colony if it occurs during the period

problems as protein, carbohydrates or

within the hive), the physiology of the

when there are no males and

water requirements (Bruneau, 2006).

bees corresponded to that of summer

consequently no insemination.

Mineral and vitamin requirements

bees, with a very short lifespan. When

Whenever the colony is visited, every

adequate supply of water can be a

It should be emphasised that an

the CO2 concentration was held steady

care must be taken not to disturb the

serious problem, especially during

but the temperature was lowered from

queen. Beekeepers must also keep

periods of heat wave, since the decline

35°C to 27°C, worker bees became

a check on the age of queens by

in the availability of water can be an

physiologically similar to winter worker

marking them. Regular renewal

important limiting factor for the survival

bees (Bühler et al., 1983).

of queens will help to maintain optimal

of colonies.

Crailsheim et al. demonstrated that

vitality, which is usually limited to

climate disturbances affect the

the first two years of their life. Colonies

Climatic factors

behaviour of nurse bees and foraging

should not be divided too late in

After a period of excessive drought,

bees, in particular with regard to

the year, so as to reduce the risk

the flowering of melliferous and

collection of nectar for the hive and

of the new colonies being insufficiently

polleniferous plants can rapidly die

food distribution within the hive.

developed in winter.

down during the summer and stop

Climatic conditions can therefore

completely. Low temperatures and

influence the development of the colony

important. To encourage colonies

especially sudden cold spells affect

and lifespan of the bees (Crailsheim

to thrive, commonsense rules must

the development of bee colonies.

et al., 1999).

apply: humidity should be kept as low

General apiary maintenance is also

Temperature is a determining factor

as possible within the hives, the

for the vitality of a colony; bees

beekeeper must insulate the hives from

maintain the brood temperature at

Beekeeping practices

the ground and ensure that rainwater

34.5 ± 0.5°C, regardless of fluctuations

It is essential for colonies to maintain

does not accumulate; the apiary must

in the ambient temperature. If,

a balanced population, given the

be kept clear of vegetation and the

however, the brood temperature is

complex organisation and working

supports used for the hives should not

raised, the emerging bees, though

relationships between their individual

retain water; the flight path must be

morphologically normal in appearance,

members. A shortage of workers, nurse

kept free from obstruction and a

present impaired learning and

bees or foraging bees can lead to

source of drinking water must be

memorisation (Tautz et al., 2003; Jones

disturbances within colonies. During

provided near the apiary.

et al., 2005). Bühler et al. studied the

beekeeping procedures a demographic

effects of CO2 concentrations and

balance must be maintained. The

spring and early summer to prevent

temperature on bees within the hive:

beekeeper’s role is to use the

or halt swarming wherever possible.

when climatic conditions were the

appropriate techniques and methods to

During swarming, nearly half – and

promote the sustainability of colonies so

sometimes as many as two-thirds –

as to ensure their annual production of

of the population leave the hive to start

honey. A lack of workers and therefore

a new colony.

Regular visits should be made in

This phenomenon may be triggered

of nutritional resources will lead to a slower development of the colonies and

by the temporary absence of a fertile

an insufficient population. If there are

queen. Visiting the colonies provides

not enough bees during the winter

the opportunity, where necessary, to:

period, they will be unable to maintain

the necessary temperature to ensure

underway: increasing the volume of the

the survival of the swarm. Loss of the

hive, creating artificial swarms, etc.;

prevent swarming from getting

2009 • 4


OIE news –

avoid swarming due to the

destruction of royal cells; –

determine the cause of colony

population decline. In temperate regions, swarming may occur up to the end of June and it may take several weeks for the colony’s population to return to normal. In addition to the fall in the number

© LeConte Pollen-gathering bee on lavander

of bees, there is also a considerable drop in honey production. Moreover,

Indeed, after collecting the honey and

These selection criteria were used

after swarming has taken place the

therefore the reserves of carbohydrate

to the detriment of the criterion of the

beekeeper must adapt the volume of

stored in the supers, the beekeeper

hygienic behaviour of bees to one

the hive to the remaining population

must provide the bees with a

another and to the brood, the latter

to minimise any unnecessary

substitute, since lack of food will lead

having been far less taken into account

expenditure of energy and avoid the

to the death of the colony. Four

than the previous two criteria.

development of parasites, and

different situations can give rise to

especially wax moths, in empty spaces.


apiculture is related to the way

The life cycle of a colony,

an insufficient quantity of food;

beekeepers use products to control the

and indeed its survival, are highly

beekeeping methods (provision of

various pathogens that can develop in

dependent on the vegetation in the

food) unsuited to the needs of a new

their apiaries. For a number of years,

environment and more specifically

strain of bees;

phenomena of resistance to acaricides

on the available sources of pollen

have appeared in a number of

and nectar. Two factors must be taken

lasting into spring, and preventing food

countries, reducing the effectiveness of

into account when setting up an apiary:


the molecules approved for use against

– the nutritional resources available

V. destructor. This resistance

throughout the season and more

alternation of short warm spells and

phenomenon is thought to be largely

especially before the critical winter

longer periods of cold weather, leading

due to the application of a control


to the opening and closing of the

strategy based on the use of a very

– the number of colonies per apiary.

swarm of bees, some way from the still

small number of acaricidal molecules in

abundant food stored in the hive

apiaries, without any alternation in their

(Haubruge et al., 2006).

use. Resistance to fluvalinate and other

A large number of colonies per site can be considered during the flowering

climatic conditions with the

The selection of queens can be a

of highly melliferous and polleniferous

acaricides has been described in many

plants. However, when food becomes

risk factor related to beekeeping

countries and could have major

scarcer the number of colonies per site


consequences for treatment efficacy

Current selection criteria are

must be adapted so that each of them

(Elzen et al., 1998; Pettis, 2004;

will have sufficient reserves of proteins

considered to be inadequate to ensure

Faucon, 2000; Shahrouzi, 2007). Thus,

and nutrients for the development of

healthy, strong and productive colonies

it could be insufficient for beekeepers

the longer-living winter bees.

(Imdorf et al., 2007). Up to now,

to apply a single treatment against

selection has always been based on:

mites in autumn, since the damage

installed in colonies, this can lead to

inflicted on the population of the colony

food deficiency and poor requeening.

specifically the absence of

When pollen traps are permanently

Another proven cause of mortality is a lack of food during the winter period.


unfavourable climatic conditions,

Another factor arising from

2009 • 4

the behaviour, and more

aggressiveness, of bee colonies; –

honey productivity.

could already be too great. Beekeepers may contaminate apiaries by:

OIE news –

resources for honey bees. The decline

However, experience has shown

healthy hives, brood or bees from

introducing bees (introduction of

in the biodiversity of polleniferous and

that, whatever the treatment, a small

affected or contaminated colonies);

melliferous plants in agricultural

but variable number of colonies will

environments is the direct consequence

retain a high level of parasitism and

colonies that have been cured but are

of a combination of two factors: the use

thus be a source of contamination and

still carrying other pathogens;

of herbicides, whether non-selective or

weakening for other colonies in the

selective, and single-crop farming,


combining healthy colonies with

reusing hives without prior


especially when it involves crops such

Of the medicinal products that have

as cereals that are of no value to bees.

received marketing authorisation,

Fields of phacelia or white clover and

Apivar NT and Bayvarol® currently

sainfoin are very often visited by

have a sufficient level of efficacy and

There have been considerable changes

foraging bees but are often mown

should therefore be given priority.

in agricultural practices during the last

before the end of flowering, resulting in

few decades.

a considerable loss of bees through

Agricultural practices

In the majority of production areas,

lack of food.

crop management has been simplified,

Colony collapse disorder (CCD) has

leading to a scarcity of some melliferous plant species and especially leguminous plants.

Colony collapse disorder been described as a syndrome

Treatment of varroosis

involving a rapid decline in a colony’s

The first treatment must be carried out

adult bee population without any dead

in late September or early October to

bees being found in or around the

these areas, to the detriment of insect-

give overwintering bees the optimum

colony (Oldroyd, 2007; Stokstad,

pollinated species (rape, field beans,

potential for survival. It must be

2007a, 2007b). In the terminal phase,

clover, etc.). It is important to

sufficiently effective to ensure that at

the queen is reported to be no longer

emphasise the damaging effects of

the end of the treatment there will be

surrounded by more than a few newly

single-crop farming, which tends to

fewer than 50 parasites within treated

emerged bees despite the fact that the

result in an alternation of over-supply

hives. Effective treatment applied at the

hive still contains reserves of food and

and shortages and is also based on

appropriate time is of prime

capped brood cells. The CCD

plants that are poor in pollen and

importance. There are several risk

phenomenon has principally been

nectar (e.g. cereals and sunflower).

factors in addition to the parasite

observed during winter losses and the

Furthermore, there is also a destructive

burden, such as the nutritional quality

bees analysed are those that have

management of the fixed features of

of the bees’ supply of pollen in autumn

survived (CCD having caused the

the landscape, such as embankments,

(for the development of fat), the

disappearance of the majority of the

hedges, roadside verges, and grassland

presence of opportunistic parasites

colony’s population). Some authors

alongside rivers and communication

such as Nosema sp., the beekeeping

have emphasised the no doubt

routes. Intensive agricultural practices

environment (degree of contamination

important role of V. destructor in this

thus result in a decline in food

from infested apiaries in the

phenomenon. The initial studies on

surrounding area), the severity of the

CCD had revealed the presence of

coming winter, etc.

numerous pathogens without being

Cereal crops often predominate in

© LeConte Pollen-gathering bee on heather

If an apiary’s colonies are located in

able to pinpoint any one specific cause

an area conducive to the early rearing

for the phenomenon (Pettis et al.,

of brood (potential source of

2007). Nevertheless, preliminary

development for the parasite), the

observations tend to show that CCD is

second treatment must be carried out

transmissible and therefore potentially

in early spring.

due to one or more pathogens.

2009 • 4


OIE news

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2009 • 4

OIE news Shahrouzi R. (2008). – L’apiculture dans le développement agricole l’exemple de la région de Rustaq en Afghanistan (www.beekeeping. com/articles/fr/apiculture_developpement_agricole _afghanistan.pdf). Shahrouzi R. (2008). – Natural and chemical

new OIE publications

control of Varroa destructor and Tropilaelaps mercedesae in Afghanistan (www.beekeeping.com/ articles/us/natural_ chemical_control_%20of_varroa.pdf). Stokstad E. (2007a). – Genomics: Puzzling decline of U.S. bees linked to virus from Australia.

Lengua azul en el norte de Europa (Bluetongue in northern Europe)

Spanish version just printed

Science, 317 (5843), 1304-1305. Stokstad E. (2007b). – The case of the empty hives. Science, 316 (5827), 970-972. Tautz J., Maier S., Groh C., Rossler W. & Brockmann A. (2003). – Behavioral performance in

Coordinated by C. Saegerman, F. Reviriego-Gordejo & P.-P. Pastoret In Spanish

adult honey bees is influenced by the temperature

Format: 16 ⫻ 24 cm

experienced during their larval development. Proc.

96 pp.

Natl. Acad. Sci. USA, 100, (12), 7343-7347. Vanengelsdorp D., Underwood R., Caron D. &

ISBN 978-92-9044-725-2 Price: € 35

Bluetongue (BT) is an infectious, viral and vector-borne disease

Hayes J. (2007). – An estimate of managed colony

of improved breeds of sheep and

losses in the winter of 2006-2007: a report

some species of deer that is of major

commissioned by the apiary inspectors of America.

international importance. The infection

American Bee Journal, 147 (7), 599-609.

is usually unapparent in cattle, which acts as reservoir for the virus. However, some serotypes such as serotype 8 (BTV-8), which recently caused a severe epizootic of BT in northern Europe, exhibit a more important virulence in cattle. Consequently, the redaction of a scientific booklet describing Bluetongue is of great utility for veterinarians and animal health professionals in the framework of an early detection of Bluetongue and other emerging diseases.

2009 • 4


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