Neonicotinoids are effective insecticides used on many important arable and horticultural crops. They are nicotinic acetylcholine receptor agonists which disrupt the function of insect neurons and cause paralysis and death. In addition to direct mortality, there are numerous sublethal effects of low doses of neonicotinoids on bees. We hypothesize that some of these large array of effects could be a consequence of epigenetic changes in bees induced by neonicotinoids. We compared whole methylome (BS-seq) and RNA-seq libraries of the brains of buff-tailed bumblebee Bombus terrestris workers exposed to field-realistic doses of the neonicotinoid imidacloprid to libraries from control workers. We found numerous genes which show differential expression between neonicotinoid-treated bees and control bees, but no differentially methylated cytosines in any context. We found CpG methylation to be focused mainly in exons and associated with highly expressed genes. We discuss the implications of our results for future legislation.

1Neonicotinoids are effective insecticides used on many important arable and horticultural 2 crops. They are nicotinic acetylcholine receptor agonists which disrupt the function of insect 3 neurons and cause paralysis and death. In addition to direct mortality, there are numerous 4 sublethal effects of low doses of neonicotinoids on bees. We hypothesize that some of these 5 large array of effects could be a consequence of epigenetics changes in bees induced by 6 neonicotinoids. We compared whole methylome (BS-seq) and RNA-seq libraries of the 7 brains of buff tailed bumblebee Bombus terrestris workers exposed to field realistic doses of 8 the neonicotinoid imidacloprid to libraries from control workers. We found numerous genes 9 which show differential expression between neonicotinoid treated bees and control bees, but 10 no differentially methylated cytosines in any context. We found CpG methylation to be focused 11 mainly in exons and associated with highly expressed genes. We discuss the implications of our 12 results for future legislation. 13

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