Effects of a Neonicotinoid Insecticide on the Growth of Honey Bee Gut Microbes

The gut microbiome plays an essential role in the overall health of organisms. However, the presence and abundance of these microbes may be altered by environmental factors, such as exposure to pesticides. The goals of this project were to understand 1) the prevalence of pesticide residues in honey bees in eastern Washington, and 2) the impact of pesticides to the honey bee gut microbiome. Accordingly, we tested bees from 24 hives among six sites across eastern Washington. High-performance liquid chromatography-mass spectrometry (HPLC-MS) was used to detect the presence and concentration of six commonly used agricultural pesticides: Carbaryl, Chlorpyrifos, Coumaphos, Cypermethrin, Imidacloprid, and tau-Fluvalinate. In addition to finding that the neonicotinoid insecticide Imidacloprid was present in 41.7% of bees tested, we found that bees from hives with Imidacloprid had significantly different gut microbiomes than bees without the pesticide, based on next-generation 16S rRNA gene amplicon sequencing. Next, we studied the effects of Imidacloprid on the honey bee gut microbiome by exposing bacteria isolated from honey bee guts against three treatments of the pesticide in 96-well plate laboratory assays. The majority of isolates tested exhibited reduced growth compared to controls, even in low concentrations of Imidacloprid. However, several isolates were robust to the Imidacloprid treatments and their growth did not differ from the control group. The combined field and laboratory data will inform hypotheses about the host-microbe-pesticide interactions that occur in the field, which can have important implications for bee, and thus ecosystem, health