Sex-dependent effects of biosynthesized nanoparticles on stored bean pests and their non-target parasitoid

The efficacy of green nanotechnology in biological control remains uncertain because of a lack of knowledge of side-effects on natural enemies and sex-dependent effects on target and non-target organisms. To address this issue, we exposed stored bean pest beetles, Callosobruchus chinensis and C. maculatus (Chrysomelidae: Bruchinae), the former infected by endosymbiont Wolbachia, and their non-target parasitoid wasp Anisopteromalus calandrae (Pteromalidae) to six types of fungus-synthesized nanoparticles (NPs): silver (AgNPs), selenium (SeNPs), silicon dioxide (SiO2NPs), copper oxide (CuONPs), titanium dioxide (TiO2NPs) and zinc oxide (ZnONPs). The nanoparticles were applied directly to the adults or indirectly via azuki beans, which served as the oviposition medium for female beetles and the sole resource for beetle larvae.Susceptibility to the nanoparticles varied across species and between sexes. SeNPs decreased the longevity of female A. calandrae, while both SeNPs and AgNPs decreased the longevity of female C. maculatus. Surprisingly, ZnONPs increased the adult longevity of C. chinensis, and SeNPs extended the longevity of male C. maculatus. When the bean surface was treated, SeNPs significantly reduced the fecundity and egg hatchability of C. maculatus, resulting in 35% reduction in emerged adults, while SiO2NPs reduced egg hatchability in both beetle species. Interestingly, none of the nanoparticles negatively impacted C. chinensis adults, likely due to the high abundance of the endosymbiont Wolbachia at this life stage. Overall, our results suggest that biosynthesized SeNPs have potential as an effective alternative insecticide for controlling C. maculatus in storage. However, the nanoparticles can increase the fitness of Wolbachia-infected pests, and also affect biocontrol agents like A. calandrae.