Comparing antennal lobe structure and glomerular organization in a specialist (Microplitis croceipes) and a generalist (Cotesia marginiventris) parasitoid

The braconid (Hymenoptera: Braconidae) wasps, Microplitis croceipes and Cotesia marginiventris, differ in their degree of host specificity. M. croceipes is a specialist larval parasitoid of Heliothis/Helicoverpa spp., while C. marginiventris is a generalist larval parasitoid of several caterpillar genera including Heliothis/Helicoverpa spp. and Spodoptera spp. Previous electrophysiological and behavioral studies by our group have showed key differences in the responses of both parasitoid species to host-related volatiles. C. marginiventris typically showed greater responses to green leaf volatiles (GLVs), whereas M. croceipes was more responsive to herbivore-induced plant volatiles (HIPVs). To investigate the neural basis underlying these differences in the responses of both parasitoid species to host-related volatiles, it is necessary to characterize their antennal lobes, which is the primary olfactory center in the insect brain. This study was conducted to compare the glomerular antennal lobe structures in females of M. croceipes and C. marginiventris, by using a combination of axonal tract tracing techniques and confocal microscopy. Here, we present a detailed description of the gross morphology of the glomerular organization of the antennal lobe of both species.