Gut Symbiont Viability in Honey Bees Exposed to Agrochemical Stressors

The honey bee gut microbiome is essential for protecting this pollinator against abiotic and biotic stressors, including the prevention of harmful gut parasites and pathogens. Previous studies have not only demonstrated a linkage of bee gut dysbiosis to increased immunodeficiencies and pathogen sensitivities, but also report the maladaptation of the gut microbiome in bees exposed to agricultural and apicultural chemistries. There are few techniques available that allow for a simple and reliable analysis of the relative proportions of live and dead gut microbes in bees exposed to these chemistries. Previous techniques for measuring gut symbiont dysbiosis are temporally limited by the digestion and excretion of non-viable, double-stranded DNA (dsDNA) from the host. Here, I will report a propidium monoazide (PMA)-based qPCR technique to quantify the antibiotic- and fungicide-mediated dysbiosis of the bee gut microbiome. Bees fed the antibiotics oxytetracycline and tylosin exhibited a 78% and 82% reduction, respectively, of gut bacteria abundance when compared to untreated bees. Similarly, gut microbes in bees fed chlorothalonil and Fumagilin-B were reduced by 44% and 68%, respectively, compared to untreated bees. These data demonstrate the bee microbiome to be depauperated within 24 h of exposure to agricultural and apicultural chemistries. These data support previous evidence that agrochemical exposures may increase pathogenicity of bee pathogens and gut parasites because of the critical role gut microbiomes play in aiding the host immune system. Fungicides, such as chlorothalonil, are not regulated to the extent of other pesticides and are sprayed during the high activity periods of pollinators when incidental exposure are more likely to occur. This PMA-based qPCR approach, coupled with DNA sequencing, is a useful technology that can rapidly identify changes in abundance and diversity of bee gut symbionts after fungicide or antibiotic exposures. In turn, a PMA-based qPCR approach can assist in the discovery of abiotic and biotic stressors of bee gut symbionts, which is an important step towards reducing the loss of a managed agricultural pollinator. Advisor: Troy D. Anderso