Pre-release analysis of the overwintering capacity of a classical biological control agent supporting prediction of establishment

Abstract

This study investigated the effect of temperature on the development and overwintering capacity of the pupal parasitoid, Diadromus pulchellus Wesmael (Hymenoptera: Ichneumonidae), a candidate classical biological control agent against leek moth, Acrolepiopsis assectella (Zeller) (Lepidoptera: Acrolepiidae) in Canada. It was estimated that 256.4 daydegrees, above a lower threshold temperature of 7.3°C, were required for D. pulchellus to complete development, from egg to adult eclosion. Laboratory and field experiments on the immature and mature parasitoids indicated that D. pulchellus overwinters primarily, if not exclusively, in the adult stage. Only adults were able to survive an entire winter under natural outdoor conditions in central Europe. Immature parasitoids developing inside their pupal hosts were capable of withstanding short periods of temperatures as low as -5°C or -10°C, but even much higher temperatures were lethal if sustained for several weeks. Among adults, females demonstrated greater cold hardiness than males. The LTime 50 at -12°C, simulating winter temperatures without snow cover, was 4-5 and 6-7 days for males and females, respectively. The LTime 50 at -4°C, simulating winter temperatures beneath an insulating snow layer, was 1-2 and 2-3 weeks for males and females, respectively, with maximum survival of eight weeks. It is likely that survival would be even greater in a natural environment where the parasitoids could select optimal overwintering sites and have the option to feed when temperatures rise enough to permit activity. Based on these results, D. pulchellus is expected to survive winters in the targeted release areas of Ontario and Quebec.

Biology and development ofAcrolepiopsis assectella(Lepidoptera: Acrolepiidae) in eastern Ontario

“…Biological control with a parasitoid has worked well in Europe, and introduction of Diadromus pulchella (Wesmael) is underway in Canada (Jenner et al 2010a;Jenner et al 2010c). These efforts are important but additional options are needed because of the immediate threat to onion production in New York State and the Great Lakes Region (Mason et al 2011).…”

The effects of periodic warming on the survival and fecundity ofDiadromus pulchellusduring long-term storage

“…The cold-stored individuals and the warm control females were of the same metabolic age and had the same exposure time to male wasps (3Á4 day old at 22928C). No males were included since mating has been observed to take place prior to cold storage (Jenner et al 2010b). Each dish was provided with a 20% sucrose solution-soaked dental wick that was replaced daily.…”

“…After a 24-h acclimation period, the wasps were provided with 15 young (B48 h old) pupae per female. Every day for 3 days, the pupae were replaced in order to prevent host-limited oviposition reduction (Jenner et al 2010b). The exposed moth pupae were incubated in Petri dishes (5.0 cm )2.0 cm) at 22928C for 25 days and wasp emergence was recorded by sex to convey post-cold storage fecundity and the sexratios of the F1 generation.…”

“…In nature, adult D. pulchellus overwinter and experimental results indicate that females can produce viable offspring after short exposures to (128C (Jenner, Kuhlmann, Cappuccino, and Mason 2010b). Occasional warm spells in winter may provide sufficient warmth for wasps in seasonal diapause to exit this state and feed.…”

Diachasmimorpha longicaudata as Biological Control agent of the Mediterranean fruit fly, Ceratitis capitata: biotic and abiotic factors affecting its implementation in citrus crops of the Mediterranean basin

“…Low temperature exposure can have lethal effects on insect parasitoids (Hance et al 2007) and, not surprisingly, overwintering survival of an introduced natural enemy is one of the major climatic obstacles to their successful establishment in new geographic ranges (Boivin et al 2006;Hughes et al 2010;Jenner et al 2010). Sublethal effects from cold temperatures can be as deleterious for biological control programs when parasitoid fitness is negatively affected, including characteristics such as development (Colinet et al 2006;Levie et al 2005;Luczynski et al 2007), body size, sex allocation, longevity, or fecundity (Pitcher et al 2002;Torres et al 2002;Hackermann et al 2008;Lopez and Botto 2005) and foraging efficiency (van Baaren et al 2005;Amice et al 2008;Bourdais et al 2012).…”