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

Bacillus thuringiensis kurstaki (Btk) is now the most used microbial agent worldwide to control lepidopteran pest in organic and non-organic crops. The extensive use of this bioinsecticide and its accumulation in the environment may become a major issue for integrated pest management programs (IPM) that include Btk and non-target species (pest parasitoids and predators) if side effects on these non-target organisms and associated food-webs occur. Here, chronic effects of the 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 parasitization behavior of female endoparasitoids toward Btk-fed larval hosts. Endoparasitoids’ developmental time in Btk-exposed hosts remained unchanged while emergence rate decreased as a function of bioinsecticide concentration, host fly strain and endoparasitoid species. In adult endoparasitoids fed Btk bioinsecticide, 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 endoparasitoids through chronic indirect host exposure and directly through food poisoning. In this context, since closely related parasitoid species may respond differently to bioinsecticide exposure, speices-specific studies must be conducted when IPM strategies combine these natural enemies with the Btk bioinsecticide.