Sublethal doses of pyriproxyfen stimulate reproduction and aggressive behavior in a non-target parasitoid wasp

Insecticides are commonly used to control populations of pests and disease vectors. However, they can have multiple unintended effects on non-target species. Assessing their impacts on the physiology and behavior of beneficial insects, such as biological control agents, is thus necessary to gain insight into the diversity and nature of such side effects. Here, we investigated the effect of sublethal doses of the endocrine disrupting insecticide pyriproxyfen, a juvenile hormone agonist, on females of the solitary ectoparasitoid Eupelmus vuilleti (Hymenoptera: Eupelmidae). These parasitoid wasps can be used as biological control agents to control the cowpea weevil, Callosobruchus maculatus (Coleoptera: Bruchidae), that infests cowpea seeds, Vigna unguiculata (Fabacea). To do so, in addition to classical measures on female fecundity and survival, we focused on female behaviors that can have important consequences on female fitness and host exploitation. First, we showed that pyriproxyfen stimulated egg production without affecting female survival. Second, we observed that low doses of this insecticide had no effect on females' exploration and host discrimination ability but stimulated their aggressiveness when fighting for host access. Although a negative impact on other life history traits cannot be ruled out at this point, these results showed low doses of pyriproxyfen can have unintended positive effects on ectoparasitoid E. vuilleti females, by enhancing at least temporarily their reproduction and host access in a situation of competition. Our work thus highlights the importance of studying the diversity of possible unintended sublethal effects of pesticides on beneficial insects.

Automated summary

Insecticides can have unintended effects on non-target species. This study investigated the effects of sublethal doses of the insecticide pyriproxyfen on parasitoid wasps and found that it increased egg production and aggressiveness, while not affecting host discrimination ability.