Effects of Bacillus thuringiensis kurstaki bioinsecticide on two non-target Drosophila larval endoparasitoid wasps

Bacillus thuringiensis kurstaki (Btk) is among the most used microbial agent worldwide to control lepidopteran pests in organic and non-organic crops. The extensive use of this bioinsecticide and its environmental accumulation may become a major issue for integrated pest management (IPM) programs that include Btk and non-target species (parasitoids and predators) if side effects on these organisms and their associated food-webs occur. Here, chronic effects of Btk bioinsecticide were explored in two Drosophila larval endoparasitoids, Leptopilina heterotoma and L. boulardi (Hymenoptera: Figitidae), indirectly on their development in the exposed host and directly on their adult longevity. Emergence rates of D. melanogaster Canton-S and Sefra host strains fed Btk bioinsecticide throughout larval development decreased at the highest concentration (10 times the recommendations), and no significant effect was observed on the parasitisation behaviour of female parasitoids toward Btk-fed larval hosts. Parasitoids' developmental time in Btk-exposed hosts remained unchanged while emergence rate decreased as a function of bioinsecticide concentration, host fly strain and parasitoid species. In adult parasitoids Btk-fed, the longevity of L. heterotoma males and L. boulardi females were reduced even at recommended spraying concentrations. Our study reports that the Btk bioinsecticide may affect non-target parasitoids through chronic indirect host exposure and directly through food poisoning. In this context, since closely related parasitoid species may respond differently to bioinsecticide exposure, species-specific studies must be conducted when IPM strategies combine these natural enemies with the Btk bioinsecticide.

Automated summary

The study explores the potential chronic effects of Btk bioinsecticide on two Drosophila larval endoparasitoids, indicating that Btk may affect non-target parasitoids indirectly through host exposure and directly through food poisoning. Different species of closely related parasitoids may respond differently to bioinsecticide exposure, requiring species-specific studies when combining these natural enemies with Btk in IPM strategies.