Differential Immune Responses in New and Old Fruit Fly-parasitoid Associations: Implications for Their Management

The oriental fruit fly, (Hendel), and marula fruit fly, (Walker), are major fruit-infesting tephritids across sub-Saharan Africa. Biological control of these pests using parasitic wasps has been widely adopted but with varying levels of success. Most studies investigating host-parasitoid models have focused on functional and evolutionary aspects leaving a knowledge gap about the physiological mechanisms underpinning the efficacy of parasitoids as biocontrol agents of tephritids. To better understand these physiological mechanisms, we investigated changes in the cellular immune responses of and when exposed to the parasitic wasps, (Ashmaed) and (Wilkinson). We found that was more resistant to parasitisation, had a higher hemocyte count, and encapsulated more parasitoid eggs compared to , achieving up to 100% encapsulation when exposed to e. Exposing to either parasitoid species induced the formation of a rare cell type, the giant multinucleated hemocyte, which was not observed in . Furthermore, compared to e-parasitized larvae, those of both host species parasitized by had lower encapsulation rates, hemocyte counts and spreading abilities and yielded a higher number of parasitoid progeny with the highest parasitoid emergence (72.13%) recorded in . These results demonstrate that cellular immune responses are central to host-parasitoid interaction in tephritid fruit flies and further suggest that presents greater potential as a biocontrol agent of and in horticultural cropping systems.