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QL 461 Journal

E834 ENT of the Entomological Society of British Columbia

Volume 91 Issued December 1994 ISSN #0071-0733

Entomological Society of British Columbia

Joint Meeting with the Entomological Society of Canada, ee 15-18 October 1995 Victoria

COVER: This ill assorted pair of noctuid moths was caught in the act and photographed by Jim Troubridge of the Pacific Research Centre, Agriculture and Agri-Food Canada. The upper, darker moth is a female Euxoa lidia locked in copulation with a male Xestia c-nigrum. They were in a mercury vapour light-trap 16 km E of Invermere, B.C., in July 1994. The photograph was digitized on an Abaton page scanner at 300 dots per inch and, for the first time, sent elec- tronically to the Graphic Designer by the Editor. He solicits good quality line drawings or pho- tographs for future insects of the year.

The Journal of the Entomological Society of British Columbia is published annually in December by the Society

Copyright © 1994 by the Entomological Society of British Columbia

Designed and typeset by UVic Graphics and printed by Printing & Duplicating Services, University of Victoria, Victoria, B.C., Canada. Text printed on 60 Ib. Halopaque Vellum Recycled Paper.


Journal of the Entomological Society of British Columbia

Volume 91 Issued December 1994 ISSN #007 1-0733

Directors of the Entomological Society of British Columbia, 1994~-95........... 22 eee 2

Gillespie, David R. and D.J.M. Quiring. Reproduction and longevity of the predatory mite, Phytoseiulus persimilis (Acari: Phytoseiidae) and its prey, Tetranychus urticae

(Acan: etranychidac) on different host plants. ........c00c00s08 bee gee eeecsennsaseeegceeds | B) Schaber, Burton D., Timothy J. Lysyk and Derek J. Lactin. Phenology of the alfalfa weevil .

(Coleoptera: Curculionidae) in alfalfa grown for seed in southern Alberta .................... 9 Cannings, Robert A. Robber flies (Diptera: Asilidae) new to Canada, British Columbia,

Yukon and the Northwest Territories with notes on distribution and habitat.................... 19

Knight, Alan. Insect pest and natural enemy populations in paired organic and conventional appie orchards in the Yakima Valley, Washington .......3...0..600c00eessececdscccessenceces 27

Taylor, S.P. and R.D. Cozens. Limiting white pine weevil attacks by side and overstory shade inate TINGE CaCONve-FOTESt REGION Geag o5 cian send ow alee ska 6 moa bea bane ha ccllnw 4 ee Giwoe® aie 37

Mayer, D.E. Effects of male to female ratio and number of females per nesting tunnel on sex ratio and number of progeny of the alfalfa leafcutter bee Megachile rotundata

Cavimemoprera: Wie CaChNidae) 6.6 ooo) nein c Boma de dak chase Shans we Gd Ge wage wend eeee nares 43 Cossentine, J.-E. and L.B. Jensen. The role of two eulophid parasitoids in populations of the

leafminer, Phyllonorycter mespilella (Lepidoptera:Gracillariidae) in British Columbia ......... 47 Syed, A. Notes on the biology and rearing of the carrion fly Prochyliza brevicornis (Melander)

MD ate rae OP MING AC)», rs og en peor vegies reese we Se ng Soe Mw aU Fp cneeas laure aes ere ote 3D Wood, L., D.A. Raworth, and M. Mackauer. Biological control of the two-spotted spider mite

in raspberries with the predator mite, Phytoseiulus persimilis ......... 00. c ccc ee eee e eee eens Die

Bradley, S.J. and D.F. Mayer. Evaluation of monitoring methods for western flower thrips, Frankliniella occidentalis (Thysanoptera: Thripidae), during the blossom period of

BGT ATA eS MINEO AIO LE Se aa 4c eed ts cca Prats Cate Sai) ase i a Sa Mw a ae ee ee ee eee oe 63 NOTES Naumann, Ken. An occurrence of two exotic ants (Formicidae) species in British Columbia ........ 69 Blatt, S.E. An unusually large aggregation of the western conifer seed bug,

Leptoglossus occidentalis (Hemiptera: Coreidae), in a man-made structure ................... 71 Fitzpatrick, Sheila M., James T. Troubridge, and Celine Maurice. Parasitoids of blackheaded

fireworm (Rhopobota naevana Hbn.) larvae on cranberries, and larval escape behaviour ........ a5)

IO UICE NWO: CON TRIBU TORS «re cns s cicaise vce go piven oes che enn edieens asus $4 une cose eeeme Je. op)



President Linda Gilkeson B.C. Ministry of Environment, Victoria

President-Elect Gail Anderson Simon Fraser University

Past-President Sheila Fitzpatrick Agriculture Canada, Vancouver

Secretary Robb Bennett Ministry of Forests, 7380 Puckle Rd., R.R.#3, Saanichton, B.C. V8M 1W4

Treasurer Shiyou Li Agriculture Canada, Vancouver

Editorial Committee (Journal) Peter Belton (Editor) H.R.MacCarthy Dave Raworth

Editor (Boreus) E.M. Belton S.E.U.

Directors K. Naumann (2nd) _L. Poirier (2nd) D. Morewood (1st) H. Philip (1st) M. Smirle (ist)

Honorary Auditor Terry Shore Pacific Forestry Centre, Victoria

Regional Director of National Society Terry Shore


Reproduction and longevity of the predatory mite, Phytoseiulus persimilis (Acari: Phytoseiidae) and its prey, Tetranychus urticae (Acari: Tetranychidae) on different host plants’




The biological control of twospotted spider mites by the predator Phytoseiulus persimilis is usually unsuccessful on greenhouse tomato crops in British Columbia. Experiments were con- ducted to determine the influence of host plant on the longevity and reproduction of the preda- tor, and on the suitability of twospotted spider mites as prey. Lifespan and reproduction of P. persimilis were lower on tomato leaves than on bean leaves but feeding on spider mites that had been reared on tomato or bean leaves had no effect on the reproduction or lifespan of P. per- similis. A strain of twospotted spider mites that came from an outbreak on a greenhouse tomato crop lived for shorter periods and laid fewer eggs when confined on tomato leaves than on bean leaves. A strain of twospotted spider mites that had been maintained on bean leaves was unable to reproduce on tomato leaves. Exudates from glandular hairs were toxic to P. persimilis. Glan- dular hairs are important in pest management on tomato crops. Their removal through breeding might make plants more susceptible to herbivores. Therefore it would be preferable to develop other methods for biological control of twospotted spider mites on tomato.


Biological control of twospotted spider mites, Tetranychus urticae Koch (Acari: Tetranychi- dae) by Phytoseiulus persimilis (Dosse and Bravenboer (Acari: Phytoseiidae) is successful on wide range of greenhouse crops throughout the world (van Lenteren and Woets 1988). How- ever, the use of this predator for biological control of T. urticae on greenhouse tomato crops has been unsuccessful in British Columbia, and elsewhere (Ravensburg et al. 1982). This has been attributed to the entrapment of P. persimilis on the glandular hairs on the stems and leaf petioles of tomato plants (van Haren et al. 1987).

It is possible that other factors associated with hairiness may also be involved in the lack of efficacy of P. persimilis on greenhouse tomato crops. Many mechanisms of resistance to insects and mites have been identified in tomato (Farrar and Kennedy 1991b). Several toxic and repel- lant chemicals, for example 2-tridecanone, are present in the glandular hairs and on the leaves of tomato plants (Farrar and Kennedy 1991b). A predator such as P. persimilis would be ex- posed to these chemicals either directly, through contact with the leaf, or indirectly, through in- gestion of prey.

Many of the mechanisms of resistance in tomato are effective against 7: urticae (Farrar and Kennedy 1991b). The degree to which the tomato plant affects reproduction and population growth in spider mite populations might aid in determining strategies for dealing with this pest.

We present here results of experiments to determine the mortality and fecundity of the preda- tory mite, P. persimilis and its prey, T. urticae, on tomato leaves.


General: The spider mite strains used in this study were maintained in continuous culture on their respective host plants. The strain adapted to feeding on bean (B-strain) originated from a commercial insectary (Applied Bio-nomics Ltd., Sidney, B.C.) where it had been reared con- tinuously on snap bean (Phaseolus vulgaris L.) for several years. The strain adapted to feeding on tomato (Lycopersicon esculentum Mill.) (T-strain) originated from an outbreak on tomato plants in a greenhouse in Surrey, B.C. in 1992.

The B-strain mites were reared on pinto beans (P. vulgaris) in pots on a laboratory bench. The


plants were inoculated weekly from stock materials obtained from Applied Bio-nomics Ltd. The T-strain mites were reared on excised tomato leaflets (cv Dombito, DeRuiter Seeds, Ohio) on styrofoam trays floating in water filled trays. The petioles of the leaflets were inserted through holes in the styrofoam into the water below. Fresh leaves were added to the trays as required.

The P. persimilis used in these experiments were also obtained from Applied Bio-nomics. Eggs of P. persimilis were produced for experiments by isolating 2 to 5 females on detached bean leaves on water-saturated cotton batting and providing them with abundant spider mites. The predator eggs were removed every 24 h. Females of P. persimilis were produced for ex- periments by rearing single eggs to adults on detached bean leaves with an abundant supply of spider mites (B-strain). The predators were examined daily, and the females were used in ex- periments within 24 h of the final molt to adult. All experiments were conducted in growth chambers at 26°C under 16h of light from cool white fluorescent tubes.

Twospotted spider mites: The effects of host plant species and spider mite strain on egg hatch, development, and survival to adult of T: urticae were determined on leaf discs on water- saturated cotton in petri dishes. Eight discs, 1 cm in diam., of each plant species were placed in rows of four on water-saturated cotton batting in each of ten, 9.2 cm square, plastic Petri plates.

A single spider mite egg (< 24h old) was placed on each leaf disc. Four bean leaf discs in each plate received B-strain mite eggs, and four received T-strain mite eggs. Four tomato leaf discs received T-strain mite eggs and four received B-strain eggs. The spider mites were ob- served daily through their development. Molts were determined by the presence of cast skins. Spider mites were moved to fresh leaf discs as required.

The effects of the plant host on reproduction in the two strains of spider mite were determined in an identical experimental design to that above, except that adult females (<24 h old) were placed on leaf discs. These females were obtained by rearing spider mites individually on their respective host plants from the protonymph stage. Females at the quiescent deutonymph stage were confined with males. On molting to adult, both the female and the male were transferred to either bean or tomato leaf discs in the experiment. Eggs were counted and removed daily. The mites were transferred to fresh leaf discs as required. Results were analyzed as a factorial design by analysis of variance (Proc GLM, SAS Institute 1992).

Predator mites: To determine if plant species affected reproduction of P. persimilis, a single female (<24 h old) was placed with a male on either a bean leaf disc infested with B-strain spi- der mites or on a tomato leaf disc infested with T-strain spider mites. Predator eggs were counted daily. Predators were transferred to fresh leaf discs as required. The results were analyzed by T- test.

Development time of P. persimilis fed on the two different strains was determined on 2 cm diam. plastic discs floating on water-saturated cotton batting in a Petri dish. Four discs were placed in each Petri dish and a single egg of P. persimilis was placed on each disc. After the eggs hatched, two of the predators were fed eggs of spider mites reared on bean plants, and two were fed eggs of spider mites reared on tomato plants. Eggs were collected with a camel-hair brush from active spider mite colonies. An excess supply of eggs was placed on each disc. Molts were determined by the presence of cast skin. The results were analyzed by T-test.

To determine if the effects seen in the previous experiment were due to plant species or spi- der mite strain, adult female P. persimilis (<24h old) were placed on styrofoam discs 2.5 cm in diam. Mixed age populations of spider mites were provided daily on fresh pieces of leaf. The prey were either B-strain spider mites on a bean leaf, B-strain mites on a tomato leaf, T-strain mites on a tomato leaf, or T-strain mites on a bean leaf. Predator eggs were counted and removed daily. Only records for those females that died of natural causes on the disc surface were used for analysis. Mites that abandoned the discs and drowned were not included in the analysis. Re- sults were analyzed by a factorial design analysis of variance (Proc GLM, SAS Institute, 1992).

The toxicity of exudates from glandular hairs of tomato to P. persimilis females was deter- mined by exposing them directly to glandular hairs, or to an aqueous solution of exudates, or to water. Twenty mites were exposed directly to glandular hairs. These were held on the tip of a moist camel-hair brush and lightly touched to 30 to 40 glandular hairs on a piece of tomato stem. They were then placed on a sheet of filter paper to recover, then held for examination. Twenty


mites, selected at random, were exposed to exudate solution. These were dipped for 4 sec in the solution, placed on filter paper to dry, and then held for examination. The solution was prepared by collecting exudate from the tips of glandular hairs, allowing this to dry overnight, then dis- solving 0.28¢ of the dried exudate in 2 ml of distilled, de-ionized water. Twenty mites were sim- ilarly dipped in distilled, de-ionized water. After 24 h, the dead mites were counted. Results were analyzed by a x2 test for goodness of fit.


Twospotted spider mites: Neither host plant nor mite strain had a significant effect (p>0.05) on the proportion of eggs hatching (Table 1). There was a significant interaction (F=18.11, p>0.001) between host plant and mite strain with respect to survival of mites from hatch to adult. There was high mortality of B-strain spider mites on tomato leaf discs, but not on bean leaf discs, and low mortality of tomato strain spider mites on both tomato and bean. Due to high mortality of B-strain mites on tomato leaf discs data on development of this strain were not in- cluded in the analysis. Instead, host plant/mite-strain combinations were used as three treat- ments in a two-way analysis of variance with sex of the mite as the other main effect. There was no interaction between sex of mite and treatment (p>0.05). Neither sex of the egg nor host- plant/mite-strain combination had an effect on the time to egg hatch (p>0.05; Table 2). Female mites took longer to develop from larvae to adults than males (F=4.71, p=0.0331). Treatment

Table 1 Mean number of eggs hatched, and survival to adult in 10 cohorts of 4 mites of each strain on bean and tomato leaf discs.

Host plant Mite strain Number hatched of four (N=10) Proportion surviving of four (N=10)

Bean Bean 3.6 0.90 Tomato epg | 0.85

Tomato Bean 3.4 0.03 Tomato ie 0.88

Mean Square Error 0.3167 0.1721

Anova Results

Host plant F (p) 1.26 (0.2685) 15.42 (0.0004)

Mite strain F (p) 0.32 (0.5776) 13.37 (0.0008)

Host x Strain F (p) 0.00 (1.000) 18.11 (0.0001)

Table 2

Mean (N, Standard Error) number of days for tomato and bean strain spider mites to complete develop- ment on tomato and bean leaf discs.

Host plant Mite strain Male Female Egg Total* Egg Total* Tomato Tomato aa 10.0a 5.0a 11.2a (7, 0.18) (7, 0.90) (19, 0) (19, 0.46) Bean Tomato 5.2a 5.2b 5.3a 5.7b (9, 0.15) (9, 0.36) (18, 0.11) (18, 0.27) Bean Bean Sl Ds 1b 5.2a 5.6b (19, 0.11) (19, 0.19) (10, 0.20) (10, 0.16)

* Time from egg hatch to molt to adult Means in a column followed by the same letter are not significantly different.


Table 3 Egg production and survival of bean strain and tomato strain adult female twospotted spider mites on bean and tomato leaf discs.

Host plant Mite strain N Number of Eggs Days Alive Bean Bean 9 49.7 13.2

Tomato 15 38.7 16.6 Tomato Bean 10 0.6 6.0

Tomato 8 2.6 10.0 Mean Square Error 27.8203 7.4501 Anova Results Host plant F (p) 22.75 (0.0001) 8.55 (0.0058) Mite strain F (p) 0.26 (0.6124) 2.43 (0.1270) Host x strain F (p) 0.55 (0.4637) 0.02 (0.8960)

Table 4

Mean development and reproduction parameters (+ standard error) for Phytoseiulus persimilis feeding on spider mites on bean or tomato leaves (N = 10).

Host plant: Bean Tomato Development Time 2.6+0.18 2.840.17 Total Eggs Laid 56.0+£5.67 38.143.34* Days of Oviposition 13.9+1.50 9.6+0.87* Lifespan 2072274 11.3+0.60* Eggs laid per day 3.0+0.46 3.4+0.28

*Significant effect of host plant (T-test, p<0.05)

(host-plant/mite-strain combination) had a significant effect on the time for development from egg to adult (F=134.96; p<0.0001). Both male and female T-strain mites required significantly longer to develop on tomato than either T-strain mites on bean or B-strain mites on bean. Spider mites produced significantly fewer eggs on leaf discs of tomato than they did on leaf discs of bean (Table 3). Spider mite lifespan was also shorter on leaf discs of tomato than on leaf discs of bean. Strain had no effect on either egg production or longevity of spider mites. Predator mites: There was no effect of spider mite (prey) strain on development time of P. persimilis on leaf discs (Table 4). Females on discs of tomato leaf laid fewer eggs over a shorter period and had shorter lives than females on discs of bean leaf (Table 4). There was no effect of host plant species on the rate of oviposition. | When P. persimilis were confined on styrofoam discs and supplied with prey on leaf pieces, there was no effect of host plant leaf pieces on the life span or fecundity of female P. persimilis (Table 5). Females that were fed B-strain mites lived for a significantly shorter time than females that were fed T-strain mites irrespective of the plant species on which the spider mites were pre- sented. Ten percent of females of P. persimilis died after exposure to water, 50% died after exposure to a solution a glandular hair exudates, and 85% died after direct contact with glandular hairs. These were significant differences (y2=22.6, p<0.05).


The twospotted spider mite, T: urticae, is broadly polyphagous. However, some spider mite populations are selectively adapted to only some of the plants that are part of their host range (Fry 1989). It is probable that no spider mite population is able to feed and reproduce on all of


the known hosts. The T-strain of spider mites used in this study originated from an outbreak on a tomato crop in a commercial greenhouse. However, it was able to use bean, P. vulgaris, as a host, and survived and reproduced better on bean than on tomato (Table 3). There were no dif- ferences in reproduction or survival between the B- strain and the T-strain on bean. On tomato, the B-strain of 7: urticae was virtually unable to reproduce. Very few immatures survived to re- produce, and females placed on tomato laid few eggs.

The reproductive abilities of the T-strain of T-urticae are so reduced on tomato that it appeared surprising that this strain was able to survive on tomato, let alone generate an outbreak. However, in laboratory culture this strain reproduced rapidly on excised leaves of tomato. The major dif- ference between the laboratory culture and the experiments described here was that many spider mites were used to start a culture, whereas a single mite was used in experiments. The large num- ber of mites used to inoculate the laboratory colony produced copious silk. Mites tend to walk on the silk and would therefore have been isolated from the leaf surface. Tomato plant glandular hairs contain many substances that are toxic to twospotted spider mites (Farrar and Kennedy 1991b). The silk would tend to protect the mites from the effects of the hairs and the larger num- ber of mites on the leaf would tend to dilute exposure to glandular hair substances.

The strain of spider mite had no effect on the fecundity of the predator, P. persimilis. In an ini- tial experiment (Table 4) fecundity was lower for females feeding on T-strain spider mites on tomato leaves than for those feeding on B-strain spider mites on bean leaves. On styrofoam discs, neither the strain of spider mites nor the plant species on which they were provided had any significant effect on reproduction in the predator. This is probably because the predators did not have to spend all of their time on the plant section provided, but could move about on the styrofoam disc, thus avoiding contact with the glandular hairs.

Predators that were fed on B-strain spider mites had shorter lives than predators fed on the T- strain mites (Table 5). In these results the interaction between host plant and spider mite strain was not significant. However, it is large enough to indicate that the significant effect of spider mite strain on lifespan could have resulted from the short lifespan (15.3 days) of P. persimilis that were fed B-strain spider mites on tomato leaf pieces. Lifespan of P. persimilis in all other treatments was greater than 18 days. Mortality among B-strain mites on tomato leaves could have reduced the number of prey available to P. persimilis. Plant resistance characters are known to affect the biology of natural enemies, even though Wheatley and Boethel (1992) showed that resistance to spider mites in soybeans (Glycine max) had no effect on P. persimilis. However, other natural enemy associations are affected by resistance characteristics in soy- beans (Orr and Boethel 1986, Rogers and Sullivan 1986, Yanes and Boethel 1983). Resistance to Manduca spp. (Lepidoptera: Sphingidae) in tomato has toxic effects on the parasitoid Te- lenomus sphingis (Hymenoptera: Scelionidae) (Farrar and Kennedy 1991a).

Table 5 Numbers of eggs laid and lifespan for Phytoseiulus persimilis females held on styrofoam floating discs and fed spider mites reared on either bean or tomato leaves (N = 10).

Host plant Mite strain Total Eggs Lifespan (days) Eggs per day Bean Bean 53:1 18.1 32 Tomato 54.9 18.9 3.1 Tomato Bean 44.2 133 3.0 Tomato 42.6 19.9 2.4 Mean Square Error 23.95 3.9 L538 Anova Results Host Plant F (p) 1.96 (0.1701) 0.51 (0.4801) 0.98 (0.3283) Mite Strain F(p) 0.00 ( .9895) 4.58 (0.0392) 0.53 (0.4714)

Host x Strain F (p) 0.05 (0.8236) 2.27 (0.1407) 0.37 (0.5475)


The host plant of the spider mite upon which P. persimilis fed did not greatly affect the biol- ogy of the predator. Females of P. persimilis confined on tomato leaflets have a shorter lifespan than females confined on bean leaves. As a consequence, the number of eggs laid is reduced, and population growth and predation would be reduced. This effect is due to contact with leaf, not the consumption of prey. Eating B-strain mites fed on tomato reduced the lifespan of P. per- similis. The cause of this was not clear.

Up to 75% of P. persimilis die moving from leaf to leaf on tomato plants (van Haren et al. 1987). If the reproduction of the remainder is reduced by up to 40% as a result of reduced life- span on leaf blades, then it would appear that enormous numbers of predators would have to be introduced into tomato crops to offset these effects

Resistance in tomato plants to spider mites can be affected to some degree by environmental factors. Increased fertilization reduces resistance through lowering both glandular hair densities and 2-tridecanone levels (Barbour et al. 1991). Glandular hair density is conversely increased in long-day, high light level conditions (Kennedy et al. 1981). Glandular hair density and other resistance factors might be reduced through breeding. However, resistance to pests based on glandular hairs is important for preventing feeding by many species of herbivores (Farrar and Kennedy 1991b), and should not be discarded for the sake of single predator/prey association. It would be preferable to develop alternative strategies for releasing and managing P. persimilis in tomato crops, or to seek other predator species that are not affected by the resistance mecha- nisms of tomato.


We thank J. Treurneit for technical assistance on parts of the project, and Applied Bio-nomics Ltd., Sidney, B.C., Canada for the supply of spider mites and predators.


1. Contribution number 516 from the Pacific Agriculture Research Centre, Agassiz, B.C.


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Farrar, R.R. Jr. and G. Kennedy. 1991b. Insect and mite resistance in tomato pp.121-142 Jn Kaloo, G. (ed.) Genetic im- provement in tomato. Springer-Verlag. Berlin, West Germany. Monographs on Theoretical and Applied Genetics.

Fry, J.D. 1989. Variation among populations of the twospotted spider mite, Tetranychus urticae Koch (Acari: Tetrany- chidae), in measures of fitness and host-acceptance behavior on tomato. Environ. Entomol. 17: 287-292.

Haren, R.J.F. van, M.M. Steenuis, M.W. Sabelis, and O.M.B. De Ponti. 1987. Tomato stem trichomes and dispersal suc- cess of Phytoseiulus persimilis relative to its prey, Tetranychus urticae. Exp. Appl. Acarol. 3: 115-121.

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Yanes, J. Jr.and D.j. Boethel 1983. Effect of a resistant soybean genotype on the development of the soybean looper (Lep- idoptera: Noctuidae) and an introduced parasitoid, Microplitus demolitor Wilkinson (Hymenoptera: Braconidae). Environ. Entomol. 12: 1270-1274.


Phenology of the alfalfa weevil (Coleoptera: Curculionidae) in alfalfa grown for seed in southern Alberta




An algorithm to forecast occurrence of four life-stage categories of the alfalfa weevil, Hypera postica (Gyllenhal), was derived from data collected in fields of seed alfalfa, Medicago sativa (L.) in southern Alberta. The algorithm assumes a linear developmental response to mean daily temperatures above a threshold of 10°C. Overwintering adults were active after the accumula- tion of 100 degree-days above 10°C (DDj9), and were scarce by 250-300 DDjo. Early larvae (instars 1 + 2) were found beginning at 120 DDj9 and their numbers peaked at 200 DD} 0. Late larvae (instars 3 + 4) were present beginning at 160 DDjo and their numbers peaked at 350 DD)j0. New generation adults appeared after 500 DDjo. In southern Alberta, alfalfa seed pro- duction is frequently combined with honey production. This algorithm enables producers to forecast the occurrence of the most damaging stage of alfalfa weevils which may require con- trol with insecticides; the advance notice enables optimal timing of treatment and also allows apiarists to minimize pesticide mortality by moving or confining their bees.

Key words: Thermal units, degree days, simulation, phenology


Pest control measures are economically justifiable only if their benefits exceed their cost (Stern et al. 1959). Normally, cost is the sum of pesticide purchase plus its application, and benefit is measured by reduced yield loss. However, other factors may enter the cost:benefit equation; this occurs in alfalfa production in southern Alberta, where seed producers frequently obtain additional income by charging apiarists to place honeybees (Apis mellifera L. (Hy- menoptera: Apidae)) in their fields. Thus, strategies to control pest insects in alfalfa seed fields must acknowledge the susceptibility of honeybees to many pesticides.

One approach to reconciling alfalfa pest management with apiculture is to give apiarists suf- ficient warning to cover the hives, or to move them, before pesticides are applied. This approach requires a method of forecasting the occurrence of the pest population. This paper presents a simple method of doing so, which is based on observed correlations between phenological events and degree-day accumulations.

In southern Alberta, the alfalfa weevil is a serious insect pest of alfalfa, feeding on shoots, flower buds and foliage during prebloom to early bloom (Hamlin et al. 1949). If not controlled it can severely reduce seed yield. Adult alfalfa weevils spend the winter in protected locations in alfalfa fields or in litter nearby. Overwintered adults become active about the time the first alf- alfa shoots appear in the spring. They feed for a few days, mate, and begin ovipositing. Peak egg density usually occurs in late May or early June, but eggs can be found during most of the sum- mer.

Rates of pre-imaginal development are temperature-dependent. Egg incubation takes 4 to 21 days. Larvae develop through the four instars in about 3 to 4 weeks. Instars 1 and 2 (early lar- vae) feed within the tightly-curled developing leaves and buds; instars 3 and 4 (late larvae) feed on expanded leaves.

Feeding damage is most obvious in mid- to late-June, concurrent with peak densities of late larvae. Defoliation is most severe toward the terminals. This type of feeding results in loss of foliage, flower buds, and nutrients, with consequent delays in plant growth and development. Quantity and quality of the seed yield may be reduced.

Late larvae inflict the greatest damage, so agricultural losses can be expected to start accu- mulating at the onset of this life stage (Dennis et al. 1986). Consequently, the timing of control tactics for the alfalfa weevil should be optimized, based on an understanding of physiological


Proportion of population in life stage

Figure 1. Observed and predicted proportion of alfalfa weevil in relation to DD 9. a) Over- wintering adults (life stage = 1): o and solid line. New generation adults (life stage = 4) A and dotted line; b) first and second instars (early larvae; life stage = 2); c) third and fourth instars (late larvae; life stage = 3). Lines are predictions made using Equations 1-3 in text.


and behavioral processes (Harcourt 1981; Whitford and Quisenberry 1990), to target this life stage. This optimization requires information on the seasonal abundance and time of occurrence of the immature stages of the alfalfa weevil through a combination of population monitoring and phenological models (Schaber and Richards 1979).

In southern Alberta, chemical insecticides are the primary method of alfalfa weevil control. Efficient use of insecticides requires that applications should be timed to target the first late lar- vae, 1.e. after they have moved to exposed positions on the leaves, but before they have caused much damage. This timing requirement establishes a potential conflict between pest control and honey production. A reliable method of forecasting the occurrence of late larvae could re- solve this conflict.

This study was conducted to develop a technique that would predict the appearance of late instar alfalfa weevil larvae in seed alfalfa fields, using southern Alberta field data. This tech- nique would enable better timing of insecticide applications in relation to insect development, and allow seed producers and apiarists more lead time to protect pollinators.

The temperature-dependence of insect development dictates that developmental models be based on thermal-unit accumulation. Simple methods for modelling phenology based on field data are available, and can be used to develop realistic models in the absence of detailed data on insect development processes (Hudes and Shoemaker 1988; Kemp and Onsager 1986; Kemp et al. 1986; Lysyk 1989). Degree-day accumulation has been used to predict peak hatch and sub- sequent activity of alfalfa weevil in forage alfalfa in southern Ontario (Harcourt 1981). How- ever, Tauber et al. (1988) have suggested that the phenology of an insect species can vary among geographic regions due to adaptation of thermal biology to local climatic conditions, so another objective was to compare phenology of the alfalfa weevil populations in southern Ontario and southern Alberta.


Algorithm development

The algorithm was developed using phenology data obtained from four research plots at the Agriculture and Agri-Food Canada Research Centre (AACRC) at Lethbridge, Alberta. Alfalfa weevil abundance was determined by taking five sweeps per plot with a 38-cm net (Johansen et al. 1979). Each plot was sampled every one to three days from 3 June to 12 August 1985; 12 May to 8 August 1987; 3 June to 20 July 1988; 3 June to 4 July 1989, and was sampled weekly from 4 June to 23 July 1990. Daily maximum and minimum temperatures (°C) were ob- tained from the AACRC meteorological station.

Alfalfa weevil phenology was modeled by correlating phenological events with degree-day accumulations using a developmental threshold of 10°C. This threshold was used because, al- though alfalfa weevil eggs hatch at 8°C, the resulting larvae do not survive even if subsequently exposed to a higher temperature (Guppy and Mukerji, 1974). Accumulated degree-days above 10°C (DDj0) from 1 January were calculated for each year by sine-wave integration (Allen 1976). Accumulated DD) on each date was rounded to the nearest 10, and samples from the 4 plots were grouped according to these rounded values. The proportion of alfalfa weevils which were adults, early larvae and late larvae were calculated for all such grouped samples, and these proportions were related to the rounded DD 9 accumulations by non-linear regression (Proc NLIN, SAS Institute 1989) as outlined below.

To provide a standardized estimate of when the weevils and larvae were most abundant, and to establish correlations between phenological events and DD;9 accumulations, their relative abundance was calculated for each plot on each day in each growing season by summing the number of weevils collected and dividing by the greatest number collected in one day for that plot in that year. These relative abundances were grouped across plots and years by the rounded degree-day values. The correlations between relative abundance and DD 9 accumulations were used to develop an algorithm to predict the appearance of the different life stages.

Alfalfa weevil phenology was divided into four stages (i): overwintered adults (i = 1), i.e.,


Proportion of population in life stage | or greater

0 0.2 0.4 0.6 0.8 1.0 ae (DD, 0" DD min ) (DDmax- DDmin ) Figure 2. Proportion of alfalfa weevil in a) life stage 2 or greater, b) life stage 3 or greater, and

C) life stage 4. Solid lines are model predictions using equation 2 and parameters estimates given in Table 1.


those present before the larval peak at 350 DD} ; early larvae (i = 2); late larvae (i = 3); and new generation adults (i = 4), i.e, those occurring after the larval peak at 350 DD jo.

The algorithm was developed as outlined below (Hudes and Shoemaker 1988). For each rounded DD jo value, the following calculations were made:

Fy = (nj +3 +ng)/2n F3 =(n3+ng)/2n F4y=ng/ =n

where nj;(i=2-4) is the number of weevils in life stage i, Xn is the total number of weevils, and F; is the proportion of insects in life stage i or later. Note that because all insects are in a life stage equal or greater than the overwintered adult stage, F) = 1.

The time trends in each F; were modelled using equation 1.

Fe=(1-0-4inppi (1)

Non-linear regression was used to obtain estimates of the parameters (aj, bj; 1 = 2 - 4). The variable t; is a scaled estimate of thermal time calculated for each life stage as:

pe DD 9 - DD mini (2) DD maxi) - PP minci In equation 2, DD ynin(i) and DD max(i) represent the approximate value of DDjo for the be- ginning and end of life stage 1, obtained by inspection of the data. The functions describing time-change in ; were then used to predict the proportion of insects in each life stage (fj):



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Il ll ees W dN


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Algorithm validation

Independently-obtained data were used to validate the algorithm. These were collected from plots in Brooks, Rosemary and Rolling Hills, Alberta (ca. 130 km N.E. of Lethbridge) by WestAg, Inc., a pest management scouting company. These plots were sampled weekly for up to 13 weeks in 1984-1988, starting the last week of May and continuing through August. Samples in a specific plot in each year were taken at approximately the same time of day to min- imize any effects of insect diurnal cycle on sampling efficiency (Johansen et al. 1979). The data consisted of weekly mean numbers of adults and of early and late larvae. The numbers of fields sampled were 48, 40, 42, 48 and 42 for 1984 through 1988. Sample counts were tabulated weekly. Daily maximum and minimum temperatures were obtained for each year from the Alberta Special Crops and Horticultural Research Center in Brooks, Alberta, and the DD jo accumulation from January | were calculated by sine-wave integration (Allen 1976). The DDjo accumulation in the middle of each week was matched with the weekly insect data. The aver- age proportion of weevils in the adult, early larval, and late larval stages was calculated for each week and compared graphically to the algorithm predictions.


Proportion of population in life stage i or greater

0 200 400 600 800 1000

Figure 3. Proportion of alfalfa weevil in commercial seed alfalfa fields. Symbols are observed mean proportion + | standard error, and lines are predictions made using Equations 1-3. a) adults, solid line is overwintered generation (life stage = 1) and dotted line is new generation (life stage = 4); b) first and second instars (early larvae; life stage = 2); c) third and fourth instars (late larvae; life stage = 3).


Seasonal phenology of alfalfa weevil

Adult weevils were first found at about 100 DD jo (Fig. 1a) and at that time were the only stage collected. The proportion of adult weevils declined from about 250 DD} and they had be- come scarce by 350 DD jo. Early larvae appeared at about 120 DD) (Fig. 1b), reached a max- imum at about 200 DD), and then declined slowly. Late larvae appeared at ca. 160 DD jo (Fig. 1c), peaked near 450 DD}, and then declined. New generation adult weevils began to appear after 400 DD jo, and increased steadily to nearly 100% of the population by 900 DD jo.

Algorithm output

Figure 1a-c illustrates the good agreeement between the algorithm output and the Lethbridge data. Estimates of the regression parameters are listed in Table 1. Coefficients of determination (r2) were 0.97, 0.84, and 0.74 for life stages 2, 3 and 4 respectively. Model predictions of pro- portions of insects in life stage i or greater are