GROWTH AND DEVELOPMENT OF COMPSILURA-CONCINNATA (MEIGAN) (DIPTERA, TACHINIDAE) PARASITIZING GYPSY-MOTH LARVAE FEEDING ON TANNIN DIETS

All larval instars of Compsilura concinnata (Meigan) (Diptera: Tachinidae) develop in the midgut of the gypsy moth [Lymantria dispar (L.) (Lepidoptera: Lymantriidae)] between the peritrophic membrane and gut wall. Parasitoid larvae placed artificially in the host haemocoel quickly moved to this characteristic position. There was a positive relationship between parasitoid size, as measured by the weight of the puparium, and the potential fecundity of female flies. When C. concinnata parasitized third-instar larval hosts, there were fewer successful multiple emergences, parasitoid larvae took longer to develop, and puparia were significantly smaller than those of parasitoids attacking fifth-instar hosts. Gypsy moth larvae grew more slowly on diets supplemented with 0.5 and 2.5% tannic acid than on non-supplemented diets. Similarly, C. concinnata females were smaller (with associated reduction in fecundity) when emerging from hosts feeding on the tannin diets than when hosts were feeding on control diets. The effect of tannic acid on the parasitoid was indirect and was the result of a reduction in host quality on the tannin diets. Reduction in parasitoid fecundity associated with tritropic interactions (among the host plant, the gypsy moth, and the parasitoid) may provide a possible explanation for the irregular impact of C. concinnata on gypsy moth populations.