Effect of transient exposure to carbaryl wettable powder on the gut microbial community of honey bees

Bees are important pollinators in agriculture. The bee population has recently begun to decline possibly due to pesticides. The bee gut microbiota strongly influences the health of bees. The gut microbiota of bees is composed of distinct members belonging to selective taxa. Chemicals like pesticides can alter the gut microbiota. The present study investigated the effect of carbaryl pesticides on gut microbiota of honey bees, which had come in contact with rapeseed plants (Brassica napus) sprayed with carbaryl wettable powder during the honey bee brood test under semi-field condition. Molecular techniques (conventional and quantitative polymerase chain reaction (PCR), clone library method, and DNA sequencing) were employed to analyze changes in the microbial communities between the pesticide-exposed and unexposed bees. Phylogenetic analysis of 16S rRNA genes of the clones from both groups, showed differences in their respective compositions of core and non-core bacteria. Both groups contained carbohydrate-degrading bacteria such as Gilliamella apicola and Lactobacillus. However, the unexposed bees harbored Alphaproteobacteria, which were absent in the exposed bees. Microorganisms found in honey bee guts such as Snodgrassella alvi and L. kullabergensis, however, were observed only in the exposed bees, but not in the unexposed bees. The difference between the two groups was distinctly recognized when copy numbers of 16S rRNA genes were compared by quantitative PCR. Results showed that the average gene copy number for the unexposed bees was higher than that for the exposed bees. This may indicate the toxic effect of pesticides on bees and gut microbiota.