1.'0

~ ~

28 1~

1.0

111112::

~W

I&i Ii.: ,W 110:

1.1

:r

......

..

::Ii.:W :W

111111.8

111111.6

25 .

~12.2 =

::W .......

1.1

k

111111.25 111111.4

OOI~ ,""

110:

~

--

:;

..

k

111111.25 111111.4

111111.6

.'

MICROCOPY RESOLUTION TEST CHART

MICROCOPY RESOLUTION TEST CHART

NATIONAL BUREAU Of STANDARDS·1963·A

NATIONAL BUREAU OF STANDARDS-1963·A

e,t ~ IU. nitedStates . ~ '"Department of STACKS

'I.

~culture/

Agricultural

Research Seil/ice

.-Iechnical

·-Bulletin

Number :t6S'8

USE ONLY

Citrus Thrips.: BiologY,Ecology, andContro·1

f

UNIVE,iBITY OF C/;\UFORNlr\

II

nl.\\fl~:;

SEP

I ..~:~r~iFT L '..J ~ •

7 1982

~'fl~~C _ :Ju .11'.

tH!!')V L' '8 t fh'l.i:_

Abstract

Contents

Tanigoshi, Lynell K., and JoyceY. Nishio-Wong. Citrus Thrips: Biology, Ecology, and Controt. U.S. Department of Agriculture, Technical Bulletin No. 1668, 17 p., iIIus. 1982.

Page

Introduction .......... , ......................•....•.

Economic impact ................... , .............. .

1

Distribution and host range ........... ,............... 2

Greenhouse mass rearing .......................•... 3

Life history .............•........•...•.............. Developmental biology .............................. 5

7

Temparature-dependent developmental rate models •... 7

Monitoring and sampling ............................. Insecticidal control .................................. 10

Ground cover tactic ............................... 10

Conventional foliar sprays ......................... 13

Central Valley ........•..............•.......... 14

Southern coast ................................. 14

California-Arizona desert ........................ 14

Inland southern California ........................ 14

Effects .of weed ecosystems on citrus thrips ..•.... . . . . . . 15

Biological control of citrus thrips ..... . . . . . . . . . . . . . . . . . . 16

Literature cited ..................................... 17

This technical bulletin reviews .and summarizes our current knowledge and research accomplishments to (1) mass rear Scirtothrips citd under greenhouse conditions on California sumac, Rhus laurina; (2) define the developmental growth parameters of S. citrf under different temperature regimes; (3) develop an inexpensive and effective emergence-dispersal monitoring trap; (4) associate thermal heat accumulation, conceived as degree-days, to the concept of thrip-days accu­ mulation; (5) valicate a nearly, reaHime, temperature-driven simulation model, SIMDEV, to predict cohort field life stage distribution; (6) evaluate the insecticidal tactic of controlling S. citd metamorphosis with ground cover, thripicidal spray applir;ations; (7) evaluate the impact of various weed ecosys­ tems and both furrow and sprinkler irrigation systems on S. citri population levels and their effects on Valencia orange fruit quality; and (8) determine the biological control role of the predaceous phytoseiid Amblyseius hibisGi ::md its potential for early season population suppression of S. cltri.

Keywords: Scirtothrips citrf, developmental rate, SIMDEV, degree-days, critical period, citrus thrips-days, cover crops, ground cover application, biological control, predaceous mite, sampling, monitoring, fruit damage index, phenology.

".IIUIIIIII.IU.II"-""l

This publication contains the results of research only. Mention of pesticides does not constitute a recommendation for use, nor does it imply that the pesticides are registered under the Federal Insecticide, Fungicide, and Rodenticide Act as amended. The use of trade names in this publication does not constitute a guarantee, warranty, or endorsement of the products by the U.S. Department of Agriculture.

Issued July 1982

Citrus Thrips: Biology, Ecology, and Control

By Lynell K. Tanigoshi and Joyce Y. Nishio-Wongl

Introduction The citrus thrips, Scirtothrips citri (Moulton), is one of three major arthropod pests of citrus, especially navel orange and lemon, found in California. The other two key pests are the California red scale, Aonidiella aurantii (Mask.), and citrus red mite, Panonychus citri (McGregor). If not properly controlled, irreparable economic and phYSiological damage from larval and aduit life stages results in stem-end ring scarring,. streaking, and splashing patterns on the shoulder and stylar end of developing fruit lets and stunting of the foliage. Due to its minute size, less than 1 mm in length, the citrus thrips remained undiscovered for many years. S. citri injury to the foliage and fruit in the early days of California's citriculture was attributed to physical causes such as freezing and wind scarring injury. In 1908, Dudley Moulton was assigned by the U.S. Department of Agriculture's (USDA) Bureau of Entomology to study the citrus thrips and its injury. In a publication entitled "The Orange Thrips," Moulton (1909) described the citrus thrips as a new species along with remarks on its life history, nature of injury, pupation site, and a tobacco extract remedy. He remarked that there were two broods a year. Moulton rightfully surmised that the first brood appeared before bloom in February and March, but was in error when he stated that the second brood appears in July through October and that this brood feeds on the matur­ ing oranges and the third and fourth foliage flushes. There are between 8 and 12 generations of citrus thrips per year in Califor­ nia. The second brood normally occurs during May. In 1918, another Bureau entomologist, J. R. Horton, published Bulletin 616, entitled, "The Citrus Thrips," which even today contains valuable field data and accurate descriptions of the life history and phenology of S. cirri. In spite of the acknowledged importance of S. citrito both California and Arizona citriculture (Tanigoshi et al. 1980), the last publication that discussed the relationships between the biology of S. citri, its chemical control, and control effects on other citrus pests was McGregor's (1944) USDA Circular 708. This cirCUlar provided a comprehensive and timely review of the citrus thrips especially written for growers, pest control per­ sonnel, and entomologists, Other than the discussion within Ebeling's (19S9) publication, "Subtropical Fruit Pests," a paucity of literature exists since McGregor's publication on either basic or applied research on S. citri, including chemical and/or biological control, treatment thresholds, and population management within the context of contemporary citrus pest management. The phenological features of S. citri have been known for oVer 50 years. Further study, however, has revealed that the bio­ logical parameters needed to conceptualize and conceive innovative (1) population models; (2) sampling and monitoring 1 Research entomologist, U.S. Department of Agriculture (USDA).

Agricultural Research Service, Boyden FrlJit and Vegetable Entomo,

logical Laboratory; and staff research associate, Department of Ento­

mology, University of California, Riverside, 92521.

2 The year in italic, when it follows the author's name, refers to Literature

Cited, p. 17.

protocols; (3) chemical control tactics within the context of integrating pest management strategies; (4) cultural control, such as ground cover management; and (5) biological control strategies through the introduction and/or augmentation of na­ tural enemies were either lacking or incomplete and, therefore, required further research. We view this technical bulletin as a companion to the earlier bulletins of Horton (1918) and McGregor (1944). In contrast to the importance of S. citrito California's citriculture, only a modest literature exists about its life style, mode of daily subsis­ tence, and methods to constrain its biotic potential within a monoculturally conceived agrobusiness. Hopefully, we can help focus on, conceptualize, and resolve the many innovative ap­ proaches to S. citri control for today's citriculturists.

Economic Impact Estimates of crop damage and loss by the California Depart­ ment of Food and Agriculture (CDFA) indicated that overall losses to the California citrus industry had increased by 35 percent during the 1972 througll1975 growing seasons. During tl1is interval, assessable yield losses remained nearly constant, in contrast to a threefold increase in control costs by 1975. This increase can be attributed to inflating operational and mana­ gerial costs and, in part, to the increased number of postpetalfall sprays required to maintain S. citri populations at 1972 levels. The 1978 CDFA estimate of citriculturallosses to insects and mites was nearly $41 rnillion. Of this value, nearly $10.5 million or 25 percent loss was attributed to citrus thrips, whereas, California red scale and citrus red mite losses were assessed at about 51 percent. These large yearly losses suggest current chemical control strategy for S. citri requires fUither scrutiny, especially if multiple treatments are required by mid-May of each year.

Distribution and Host Range Locality records (fig. 1) and the foHowing host plant associations indicate that the citrus thrips is Nean::tic and is native to the southwestern United States and northwestern Mexico.

Cultivated host plants Navel orange Valencia orange Lemon Lime Grapefruit Tangerine Avocado Grape Deciduous fruit trees

Noncultivated host plants California sumac Liveoak Mesquite Willow California pepper tree Buckthorn Creosote bush Chamise Fir Magnolia tree California laurel

Bailey (1964) believed S. citri to be a native species that has found Citrus spp. to possess the biological prerequisites for near optimum growth and development. This host favorability and associated climatic features will potentially result in numer­ ical increases of S. citri if left unchecked. He also felt that the

RANGE

MAP OF

CITRUS T H RIP S

INC A 1I FO RN I A

.

Figure 1.-Distribution of Scirtothrips citri (Moulton) (modified from Horton 1918).

liveoak (Quercus spp.) is probably the native host. Ewart (per­ sonal communication) believes California sumac, Rhus laurina (Nutt.), to be an equally good candidate for the native host designation. R. laurina is commonly found in the coastal and inland valle~'S of southern California. Stands of sumac can be found adjacent to citrus orchards throughout its range. Since 1918, when Horton published a map showing the known distri­ bution of S. citri, this insect has established populations within the coastal areas of Santa Barbara, Ventura, and San Diego Counties, and the desert valley areas of Coachella, Imperial, and Yuma in Imperial County and Yuma County, Ariz. (fig. 1). The natural habitats of the citrus thrips are generally the tem­ perate Grassland Biome of the Central Valley, Coastal Chapar­ ral Biome, and the irrigated areas of the Sonoran Desert Biome. Citrus thrips is also known from Maricopa County, Ariz., and the States of Baja California Norte and Sonora, Mexico These areas are either in the Chaparral or irrigated Sonoran Desert Biomes.

Greenhouse Mass Rearing A system was developed by Tanigoshi and Nishio-Wong (1981) ~o mass rear S. citr; within environmentally controlled green­ houses. The system, as conceived at the ARS Boyden Ento­ mological Laboratory, Riverside, Calif., consists oftwo separate

2

greenhouses. Both greenhouses, shown in figure 2, measure 5.5 by 8.2 m with the house on the right divided into four rooms, each about 2.1 by 4 m. All the interior walls ofthe compart­ mentalized greenhouse consist of 150-mesh/inch stainless steel screen. The.environment of each greenhouse, precluding the watering system, is controlled and programed by an en­ vironmental control system. Heat is provided by a gas-fired, low static pressure propeller fan heater. Cooling is accomplished with a 75,000-Btu evaporative cooler fitted with particulate and smog filters and four motorized shutters placed near the corners of the greenhouse. High-volume air circulation at 6,000 Wlmin is provided by turbulalor jet fans. Amelioration of intense solar radiation, between April to October, is.accomplished with a whitewash spray formulated with 3.8 L of water, 0.45 kg of calcimine, plus 20 ml of white glue. Every potted plant is watered with a drip emitter through which essential nutrients are injected at the rate of 1 part nutrient to 200 parts water (Hoagland and Amon 1950). Temperature .extremes in the greenhouses can range from about 21 ° to more than 40°C. Hundreds of R. laurina shrubs can be propagated in redwood nursery flats filled with the standard University of California, Riverside (UCR), soil-sand-peatmoss mix (Matl­

< C

.4

2

EGG

1 ST

2ND

PUPA PUPA

LIFE STAGE Figure 10.-Scirtothrips citri life stage development at alter­ nating temperatures. Length of each bar represent develop­ mental period for designated life stage.

BN-49131

Figure 12.-PVC-acetate Scirtothrips citri emergence trap.

BN·49132

Figure 11.-Scirtothrips citrl emergence box trap (after Reed and Rich 1975).

BN-4S'130

Hgure 13.-Machine used to apply an even coat of Tangleioot to both sides of clear acetate plates.

9

of S. citri present at the beginning of the sample periocl to the number present at the end of the period, then, dividing the sum by 2 and multiplying the result by the number of elaps&d days between samples.

Table 3. -Mean weekly catches of S. citri captured on Reed­ Rich and PVC-acetate traps placed under 'Washington' navel orange, Riverside, Calif., 1979 (Tanigoshi and Moreno 1981)

~~._. _________ .-.lL~_larv_Cle;_,t>,_ ==~~9u Its_l .._.. ______.......__....~

~!~_1..6_

_ . _~..!X..3Q....

_July 23

Trap~ __. _~ .. .l::....~.,~__ _. ~.., __ P, .. Reed-Richl PVC-acetate

13.1 10.1

3.4 2.8

17.3 20.6 - .. -

-~

2 9.3

____'=---~ ft.__ .. _L_ 141

17.4 ..12.0 --_.­ .. ~---

.,' Au~~_..

12.2 28.7 7.2- - . 27.2 -­

----~-. ~-

A 17.5 21.6

-"

1 Counts were reduced by a factor of 65 percent.

20enotes significant difference. P c_ 0.05. using Student's t-test.

Insecticidal Control Ground Cover Tactic

Figure 14. -Clear vinyl folder facilitates the job of assessing SClrtothrips citn population levels on Tanglefoot coated acetate plates.

5000

ORANGE

BN·49129

Recent studies in South Africa by Milne and de Villiers (1977) have shown the feasibility of using soil applications of systemic pesticides for control of the South African citrus thrips, Scirto­ thrips aurantii Faure, on citrus. Dimethoate 40 percent emulsifi­ able concentrate (Ee) was applied at a rate of 20 kg AI/ha in irrigation basins at 20 percent petalfall. Percent mean cullage at harvest was 3.5 percent as compared with a foliar application of parathion and Abate which, when coming off the packing belt, packed out at 0.9 percent. These percent cullage figures were not significantly different at the 5-percent probability level.

COVE­ CHASE

1979 - NAVEL

*

4000



+ .....-..­

...







28

5 JUNE

~

/.

f/)



4: 0

3000



f/) Q..

c.::

:r:: ~

f/)

2000

::> c.::

./._.

~

U II

1000

)/



26 18 APRil

4

11

17 MAY

Figure 1S.-Charting the use of the PVC-acetate trap to monitor early season citrus thrips populations and to evaluate the impact of a 1.1 kg Al/ha application of dimethoate on May 17. I c immatures, A - adults, • '" 100 percent bloom drop.

10

The significance of the South African study was to eliminate foliar application of pesticides potentially destructive to benefi­ cial parasitoids, predaceous insects, and mites. S. citri is known to pupate in soil and organic debris found mostly under the tree canopy. Studies conducted by Tanigoshi et aJ. (1982) on 'Washington' navel, from 1978 to 1980, to evaluate the notion that this propensity to pupate in soil and ground cover accumu­ lation may be the "weak link" in the citrus thrips life cycle toward which control tactics should be focused. The following granular and liquid formulations of organophosphate and carbamate type pesticides (table) were selected based on their toxicity (LOso )' pests controlled, phytotoxicity, and residual persistence parameters.

Chemical

Active ingredient (kg/ha)

Chforpyrifo$ 15G Chlorpyrifos 4EC Do. Do. Fonofos4EC Carbofuran 10G Carbofuran 4F Do.

6.7 6.7 4.1 3.4 4.5 5.6 6.7 4.1

1 Liters

Chemical

Active ingredient (kg/ha)

Carbofuran 4F FMC 35001 4EC Oxamyl10G Oxamyl2L Do. Do. Weed oil (50 pct)

3.4 6.7 5.6 5.6 4.5 3.4 16 . 1

biota, e$pecially arthropods; and (4) residual activity of the various \!ompounds under orchard conditions. We have chosen to detail the third year's results concerning control of first and second generation S. citri on navel orange. A 2.5-ha block of 12-year-old 'WaShington' navel orange located in Woodcrest, Calif., was selected for the purposes outlined above. Tree spacing was 4 by 6m; water was provided with sprinkler irrigation. All 64 trees in each of the plots received dosage rates equivalent to: plot 1 = 6.7 kg AI/ha carbofuran 4F, plot 2 = 6.7 kg Allha FMC 35001 4EC, plot 3 = 4.5 kg Altha fonofos 4EC, and plot 4 = 4.1 kg Allha chlorpyrifos 4EC. Plot 5 is the untreated control. These formulations were applied with a high-pressure sprayer specially b:'passed to produce 18 psi pressure through a.,handwand delivering 2.5 L of water per minute. Each plot was sampled weekly to 9 September 1980. Within-tree population levels were monitored with the PVC-acetate ground trap. Samples were taken from the corner trees and central four trees in each plot (figs. 16 and 17). Petalfall was essentially completed between 22 and 27 April, and the critical period was considered terminated by about 7 July. By the end of July, population levels from all five plots demonstrated a marked S. citri numerical increase. Obviously, the effective residual persistence of the pesticides was negli­ gible 3 weeks beyond the terminus of the critical period; how­ ever, within the 8-week "critical period" (fig. 18), emergence PVC-acetate traps revealed reductions in accumulated citrus thrips-days for both life forms by 1 July of 2.2-,4.8-, 6.9-, and 11.2-fold for carbofuran, chlorpyrifos, FMC 35001, and fonofos, respectively, when compared with the untreated control plot.

per hectare.

The purpose of our monitoring and sampling procedure was to demonstrate: (1) control of first and second generation citrus thrips; (2) duration of effective control; (3) effects on soil micro­

4 V)

CON TROl

>

-

­

< C

V)

a.. ~

+•

2

lO'xl

, , , ,

V)

2

"

..........."'::::.............. I ".

0" ,._._._•.,:::0:'_."-'-":-'-'-'-' .-'-'-'

, ,

I

t

......

i i i

,,­

/.

6

t­ 3

,.' .'"

u

"

2

+

*

I ,.,"

oJ·--·--·--·--·..•.. ·~·--I ..Ir.=:::::::~::::~~~ i i i

25

M

i

B

A

,

i i i

22

6

i i i

20

M

i



3

17

J

- : - . ,• • • • • • • • - : - _ .....

i i i

15

,.

J

12

A

26

B

6

1 . . ",. .

4,

I 1O'x2~ ~", * I .......... . .' QJ._._._._._.........._..............RI,_--··­ I

I

9

2'5

S

M

'

B'

..

",

,.

"

2'2

'

A

(,

'2'0

M

3

1'7

J

I

15

J

Figure 17.-Accumulations of S. citri-days on PVC-acetate traps placed under navel orange tree':; at Woodcrest, Calif., in 1980. Stars indicate dates for 100 percent bloom drop; vertical lines denote ends of critical period; and arrows indicate treatment days.

~

~

;/./._.

AEC, 5.0kg AI/he

t

i i i

29

.

10

. " I y' "",."

4

lO'xl

CHLORPYRIFOS

.",.,.'

,j'

5

iii

12

FONOFOS 4E, -i.5kg AI/he

.,.,,~

. ' ",' * " , , , , , ... _._ ...... _._.::-'-'-'-' I " " .... oJ._._._'_'r.'-'-'-'-'~

10'.1

7

::J

ex:

3

y

3

:x: t-

y'I

4

~

)..

2'9

12

2'6

A

9 S

.... 250

RIVERSIDE, CA.

IMMATURES