Intraspecific variation in bumblebee microbiome sensitivity to pesticides

Population declines of wild bees are linked to multiple stressors including the widespread use of pesticides which bees consume while foraging from both wild and cultivated plants. Although exposure to agricultural chemicals can be harmful to many aspects of bee health, their impact on the microbiome is less understood. Here we ask: does exposure to multiple pesticides predicts changes in the wild bee microbiome and is response site-specific? We collected yellow-faced bumble bees (Bombus vosnesenskii, n=202) from three sites in Northern Nevada: a suburban park, a scrubland shoreline, and an alpine meadow. Bees were maintained on a sucrose diet containing either the insecticide imidacloprid, the fungicide tebuconazole, the herbicide glyphosate, the combination of all three chemicals, or a control. Upon mortality (or after 20 days), bee’s guts were dissected for 16s sequencing. We found site-level differences in gut community composition (PERMANOVA; Pseudo-F stat = 3.09, p = 0.004), and bacterial abundance showed site-specific responses to pesticide exposure. For example, abundance of the core symbiont Schmidhempelia did not vary by treatment in alpine bees (GLM, x²=2.14,
p=0.70), but its abundance increased at our shoreline site relative to control bees (GLM, x²=8.50, p=0.05) and decreased in fungicide-exposed bees at the suburban site relative to control bees (GLM, x²=4.20, p=0.03). These results highlight the importance of considering population of origin in studies examining the effects of pesticides on wild bees.