Worldwide used bio-insecticides Cry1Ac toxin has no detrimental effects on Episyrphus balteatus but alter the symbiotic microbial communities.

Hoverflies, capable of abilities providing dual ecosystem services including pest control and pollination, are exposed to insecticidal proteins from transgenic plants via pollen and prey aphids. However, the effects of such exposures on hoverflies have never been adequately assessed. Here, we investigated impacts of the most widely used biotoxin Cry1Ac on a representative hoverfly species Episyrphus balteatus through food chain transmission and active toxin exposure. The results showed Cry1Ac can be transmitted into E. balteatus through feeding on Aphis gossypii reared by Bt insect-resistant cotton variety expressing the Cry1Ac toxin, but the biological parameters of E. balteatus including survival rate, growth, development, reproductive capacity, and detoxification-related gene expression, were not significantly affected. Furthermore, the exposure to high-dose Cry1Ac toxin (500 μg/mL) resulted in slight increase of 16.67 % in the activity of detoxification and antioxidant enzyme catalase in E. balteatus and inhibited the egg hatching, partially inducing stress responses. Notably, the exposure to Cry1Ac toxin disrupted the microbiota homeostasis in E. balteatus, and the relative abundances of three dominant symbiotic bacterial genera (Cosenzaea, Wolbachia, and Commensalibacter) in E. balteatus exhibited a 10 % ~ 40 % fluctuation under Cry1Ac toxin stress. Taken together, these results suggest Cry1Ac toxin is not lethal to E. balteatus, but it poses a potential threat to its endosymbiotic bacteria.