Deleterious effects of mild simulated overwintering temperatures on survival and potential fecundity of rose-galling Diplolepis wasps (Hymenoptera: Cynipidae)

Prepupae of the rose galling Diplolepis spinosa from areas with relatively cold winters in southern Canada, and Diplolepis variabilis from a milder locale in western Canada, were used to test the hypothesis that mild winter temperatures are detrimental to the survival and potential fecundity of insects. Prepupae of D. spinosa held within or removed from their galls were exposed to simulated overwintering temperatures (-22, 0, 5, or 10degreesC) for approximately four months before measuring their survival, body size, and potential fecundity. Similar studies were conducted using prepupae of D. variabilis that were removed from their gall and subjected to 0degreesC or 10degreesC treatments. Diplolepis spinosa, with or without their galls, averaged 66% more mortality at 10degreesC than at 0degreesC. Female D. spinosa that survived the 10degreesC treatment had 32% fewer eggs than those held at 0degreesC. In contrast, there was no difference in survival or numbers of eggs between D. variabilis held at 0degreesC and 10degreesC. Body size of adult females and size of eggs did not differ among temperature treatments for either species. We conclude that mild overwintering temperatures may be detrimental for insects by raising their metabolism, and consequently reducing energetic reserves needed for development to the adult stage and subsequent production of eggs the following spring. (C) 2003 Wiley-Liss, Inc.