Evaluation of sequential exposure of irradiated hosts to maximize the mass rearing of fruit fly parasitoids

Abstract

A series of evaluations were carried out to assess the feasibility of sequentially exposing tephritid hosts to a primary and a secondary parasitoid to ascertain if the larvae not parasitized by the primary parasitoid could be attacked by the secondary parasitoid in the pupal stage, thus optimizing the mass production of two or more species of parasitoids. Larvae or pupae of Anastrepha ludens (Loew) were exposed either to no parasitoids, the larval parasitoid Diachasmimorpha longicaudata (Ashmead) (primary parasitoid), the pupal parasitoids Coptera haywardi (Oglobin), Dirhinus sp., and Eurytoma sivinskii (Gates & Grissell) (secondary parasitoids), or sequentially to combinations of both the larval and pupal parasitoids. As part of all evaluations, host larvae were either irradiated or unirradiated. Typically, host larvae are irradiated under parasitoid mass rearing to avoid fly emergence from unparasitized hosts. Results show that a second host exposure did not increase parasitoid production mainly due to a high incidence of mortality caused by multiparasitism. With the exception of pupae exposed to C. haywardi obtained from irradiated larvae previously exposed to D. longicaudata, multiparasitism was around 50%. This resulted in a reduction in emergence of both parasitoids. To some extent, pupal parasitoids discriminated among pupae, preferring to oviposit in pupae that were not superparasitized previously by D. longicaudata. Notably, pupae resulting from irradiated larvae were not appropriate for the development of C. haywardi. In contrast, in the cases of Dirhinus sp. and E. sivinskii, adult parasitoids did emerge from pupae resulting from irradiated larvae, although emergence was significantly lower than when pupae from unirradiated larvae were used. Our findings offer critical insights for fine-tuning the possible use of sequential host exposure to maximize parasitoid mass production.