Host-parasitoid developmental interactions are modulated by venom components of Aphidius ervi (Hymenoptera, Braconidae)

Aphidius ervi regulates physiology and reproduction of the pea aphid, to enhance its nutritional suitability for the developing offspring. Here we investigated the functional role of the main components of A. ervi venom, Ae-γ-glutamyl transpeptidases (Ae-γ-GTs), using RNA interference. The suppression of Ae-γ-GTs was obtained through microinjection of dsRNA solution in A. ervi female pupae, and their relative expression was checked by qRT-PCR. Parasitism by knocked down females induced a significant increase of aphid size and bacterial load of the primary aphid’s symbiont Buchnera aphidicola. Similarly, both A. ervi larvae and teratocytes showed a significant increase in size. The silencing of Ae-γ-GTs significantly reduced the host castration which resulted similar to that induced by wild type parasitoid females. Parasitoid adults were of larger size, but this trait was associated with a reduced survival and fecundity, suggesting a trade-off of the body size increase. These results shed light on the role of venom in the intricate network of interactions among the parasitoid, the host aphid and its symbiont, which finely orchestrate the development of parasitoid’s offspring.