The effect of maternal factors of Cotesia glomerata (Braconidae) on its larval competitor Hyposoter ebeninus (Ichneumonidae)

Parasitoids of different species frequently develop in the same host, a phenomenon referred to as “multiparasitism”. Although the outcomes of multiparasitism have been well-documented in the literature, the underlying mechanisms, particularly the substances injected by a female parasitoid along with her egg(s) into a host during parasitism, remain relatively unexplored. Previous work on parasitoids associated with the cabbage white butterfly, Pieris brassicae (Lepidoptera: Pieridae) has shown that the larva of the solitary parasitoid Hyposoter ebeninus (Hymenoptera: Ichneumonidae) has a higher survival but a longer development time when competing with the gregarious parasitoid Cotesia glomerata (Hymenoptera: Braconidae). In this study, we hypothesize that the maternal factors injected by C. glomerata are responsible for the effect on the performance of H. ebeninus larvae. This hypothesis was tested using P. brassicae caterpillars first parasitized with H. ebeninus and then injected with C. glomerata maternal factors, or parasitized by both parasitoids. Our results suggest that C. glomerata maternal factors are at least partially responsible for the reduction in H. ebeninus developmental mortality (likely through effects on the immune response of the host caterpillar), but does not seem to affect its development time. We discuss these results and the current knowledge of maternal-factor-mediated parasitoid interactions.