Effects of Condensed Tannins and Catalpol on Growth and Development of Compsilura concinnata (Diptera: Tachinidae) Reared in Gypsy Moth (Lepidoptera: Lymantriidae)

Condensed tannin is generally considered an example of a quantitative plant allelochemical defense, and catalpol an example of a qualitative chemical defense. The effects of these compounds on the growth and survival of a tachinid parasitoid, Compsilura concinnata (Meigen), reared in the gypsy moth, Lymantria dispar (L.), were compared. Each chemical was incorporated into synthetic diets in a range of ecologically relevant doses and fed to host larvae. Larvae were fed in each of two ways: immediately after parasitization (one day after fourth instar molt), and from egg hatch onward. Growth and survival of unparasitized gypsy moth larvae on test diets were also monitored. No significant effect of either catalpol or condensed tannin on C. concinnata growth or puparial survival was observed. Tannin did lengthen development time of unparasitized host larvae from fourth stadium onward, and lowered pupal weights of larvae fed tannin from egg hatch onward. Catalpol had no significant impact on overall gypsy moth larval development, indicating that this insect is able to compensate for the reduction in weight gain reported to be caused by catalpol in younger larvae. Mortality in all experiments was insignificant. It appears that these phytochemicals are more similar in their effects on the parasitoid than was predicted based on their roles as toxins and digestibility-reducers in herbivores. The data also suggest that generalist tachinid parasitoids such as C. concinnata may be more tolerant of allelochemicals in their host's diet, than their hymenopteran counterparts.