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Neonicotinoid insecticides are potent agonists of nicotinic acetylcholine receptors and are a major factor in the decline of pollinators worldwide. Several studies show that low doses of this neurotoxin influence honey bee physiology, however, little is known about how insecticides interact with other environmental variables. We studied the effects of two neonicotinoid Imidacloprid doses (IMD, 0, 2.5, and 10 ppb), and three temperatures (20, 28, and 36°C) on gene expression in the brains of worker honey bees (Apis mellifera). Using qRT-PCR we quantified the expression of eight key genes related to the nervous system, stress response, and motor and olfactory capacities. Gene expression tended to increase with the low IMD dose, which was further intensified in individuals maintained in the cold treatment (20°C). At 20°C the octopamine receptor gene (oa1) was underexpressed in bees that were not exposed to IMD, but overexpressed in individuals exposed to 2.5 ppb IMD. Also, heat shock proteins (hsp70 and hsp90) increased their expression at high temperatures (36°C), but not with IMD doses. These results suggest that despite the low insecticide concentrations used in this study (a field-realistic dose), changes in gene expression associated with honey bee physiological responses could be induced. This study contributes to the understanding of how neonicotinoid residual doses may alter honey bee physiology., (Copyright © 2020. Published by Elsevier Ltd.)

Bees are key regulators in the maintenance of global biodiversity and food security. Overwhelming evidence has shown elevated colony losses for honey bees and a decrease in the abundance of other pollinators. Insecticides of the neonicotinoid type have been associated with these losses, but few studies have explored how residual exposure doses affect the queen's energy metabolism. Here, we studied how a residual dose of neonicotinoid (imidacloprid), combined with reproductive status (virgin and inseminated) affects honey bee queen's metabolism. We conducted the same experiment in two geographical locations (Chile and Colombia) and found a strong reduction of standard metabolic rate (SMR) in insecticide-treated queens (Chilean queen bees 11.3% reduction in watt output; Colombian queen bees 11.7% reduction in watt output). No effects were found when comparing reproductive condition on SMR. We will highlight the possible consequences of a weak honey bee queen's performance on colony stability. [ABSTRACT FROM AUTHOR]