Developmental stages and kairomones from the primary parasitoid Cotesia marginiventris (Hymenoptera: Braconidae) affect the response of the hyperparasitoid Mesochorus discitergus (Hymenoptera: Ichneumonidae) to parasitized caterpillars

The hyperparasitoid Mesochorus discitergus (Say) discriminates among unparasitized Plathypena scabra (F.), Helicoverpa zea (Boddie), Pseudoplusia includens (Walker), and Spodoptera frugiperda (J.E. Smith) caterpillars and those parasitized by the primary parasitoid Cotesia marginiventris (Cresson). M. discitergus females detect C. marginiventris within 1 h after parasitism of either P. scabra (green cloverworm) or S. frugiperda (fall armyworm). The time spent handling parasitized green cloverworms and fall armyworms increases until after hatch of the C. marginiventris egg. C. marginiventris eggs did not appear to be suitable hosts for the hyperparasitoid, whereas first instars were. Therefore, the difference in handling times between caterpillars with egg or larval C. marginiventris may be related to the time a M. discitergus female needs to locate and parasitize a C. marginiventris larva. Results of injecting crude extracts from the C. marginiventris calyx region, or venom gland and venom reservoir, into fall armyworm larvae suggest that the venom gland extract causes changes in the hemocoel of fall armyworms that are used by M. discitergus as kairomones to discriminate between parasitized and unparasitized caterpillars. Our results do not exclude the possibility that calyx fluid too has kairomonal properties.