Honey bee Apis mellifera larvae gut microbial and immune, detoxication responses towards flumethrin stress

Mites are considered the worst enemy of honey bees, resulting in economic losses in agricultural production. In apiculture, flumethrin is frequently used to control mites. It causes residues of flumethrin in colonies which may threaten honey bees, especially for larvae. Still, the impact of flumethrin-induced dysbiosis on honey bees larval health has not been fully elucidated, and any impact of microbiota for decomposing flumethrin in honey bees is also poorly understood. In this study, 2-day-old larvae were fed with different flumethrin-sucrose solutions (0, 0.5, 5, 50 mg/kg) and the dose increased daily (1.5, 2, 2.5 and 3 μL) until capped, thereafter the expression level of two immune genes (hymenoptaecin, defensin1) and two detoxication-related genes (GST, catalase) were measured. Meanwhile, the effect of flumethrin on honey bee larvae (Apis mellifera) gut microbes was also explored via 16S rRNA Illumina deep sequencing. We found that flumethrin at 5 mg/kg triggered the over expression of immune-related genes in larvae, while the larval detoxification-related genes were up-regulated when the concentrations reached 50 mg/kg. Moreover, the abundance and diversity of microbes in flumethrin-treated groups (over 0.5 mg/kg) were significantly lower than control group, but it increased with flumethrin concentrations among the flumethrin-treated groups. Our results revealed that microbes served as a barrier in the honey bee gut and were able to protect honey bee larvae to a certain extent, and reduce the stress of flumethrin on honey bee larvae. In addition, as the concentration of flumethrin increases, honey bee larvae activate their immune system then detoxification system to defend against the potential threat of flumethrin. This is the first report on the impact of flumethrin on gut microbiota in honey bees larvae. The findings revealed new fundamental insights regarding immune and detoxification of host-associated microbiota.