Abstract
Over the last decade, the persistent dwindling of the populations of honey bees has become a growing concern. While this phenomenon is partly attributed to neonicotinoids (NEOCs), chronic exposures to these insecticides at environmentally-relevant concentrations are needed to fully estimate their implications. In this study, honey bees were orally exposed for 10 days to low field-realistic concentrations of NEOCs known for their effects on the cholinergic system (imidacloprid – IMI or thiamethoxam – THM). Selected biomarkers were measured such as acetylcholinesterase (AChE) activity, lipid peroxidation (LPO), α-tocopherol as well as several forms of vitamin A (retinoids) and carotenoids. Bees exposed to IMI showed lower levels of two carotenoids (α-carotene and α-cryptoxanthin) and α-tocopherol. The THM exposure increased the oxidized vitamin A metabolites in bees conjointly with the LPO. These results could be the consequence of a pro-oxidant effect of NEOCs and were observed at levels where no effects were recorded for AChE activity. This study reveals that exposure to low levels of NEOCs alters the carotenoid-retinoid system in honey bees. This would merit further investigation as these compounds are important in various aspects of bees’ health. Overall, this study contributes to the development of biomonitoring tools for the health of bees and other pollinators.
Highlights
Global honey bee loss has become a prior economic and environmental concern
NEOCs residues were found in honey bee tissues, confirming the exposure of bees to these insecticides through their foraging activities
Honey bees are exposed to NEOCs mainly through pollen, nectar and guttation fluids
Summary
Global honey bee loss has become a prior economic and environmental concern. While there is a consensus that this situation is the result of several factors, abnormal bee deaths have been associated with the widespread use of neonicotinoids (NEOCs). Commercialized in the 1990 s as systemic and broad-spectrum insecticides, NEOCs are intended for agricultural pest management Given their selective toxicity for insects and their wide array of applications (e.g., seed coating, foliar spray and soil drenches), they became the most widely used class of insecticides and account for more than 23.7% of the world market share[1]. When honey bees were fed with technical or commercial NEOCs formulations, observed side effects were reported on foraging activity[6], memory[7], immunity[8], reproduction[9] and development[10]. THM promotes oxidative stress in honey bees as shown by the increased activity of catalase and glutathione S-transferase[13]. The present paper is the first to investigate the NEOCs-induced alterations in the honey bee’s carotenoid-retinoid metabolism under laboratory controlled conditions
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