Abstract
Overwinter colony mortality is an ongoing challenge for North American beekeepers. During winter, honey bee colonies rely on stored honey and beebread, which is frequently contaminated with the neonicotinoid insecticides clothianidin and thiamethoxam. To determine whether neonicotinoid exposure affects overwinter survival of Apis mellifera L., we chronically exposed overwintering field colonies and winter workers in the laboratory to thiamethoxam or clothianidin at different concentrations and monitored survival and feed consumption. We also investigated the sublethal effects of chronic thiamethoxam exposure on colony pathogen load, queen quality, and colony temperature regulation. Under field conditions, high doses of thiamethoxam significantly increased overwinter mortality compared to controls, with field-realistic doses of thiamethoxam showing no significant effect on colony overwinter survival. Under laboratory conditions, chronic neonicotinoid exposure significantly decreased survival of winter workers relative to negative control at all doses tested. Chronic high-dose thiamethoxam exposure was not shown to impact pathogen load or queen quality, and field-realistic concentrations of thiamethoxam did not affect colony temperature homeostasis. Taken together, these results demonstrate that chronic environmental neonicotinoid exposure significantly decreases survival of winter workers in the laboratory, but only chronic high-dose thiamethoxam significantly decreases overwinter survival of colonies in the field.
Highlights
Honey bee colony mortality is most prevalent during the winter months in temperate climates, and, since 2007, Canadian beekeepers have experienced average overwinter losses in excess of the15% economically sustainable threshold [1]
We demonstrated that chronic experimental neonicotinoid exposure during the Saskatchewan winter significantly decreased overwinter survival of (1) honey bee colonies in the field
Our study shows that colonies overwintering in Saskatchewan on canola honey and beebread low risk of mortality from chronic neonicotinoid exposure
Summary
Honey bee colony mortality is most prevalent during the winter months in temperate climates, and, since 2007, Canadian beekeepers have experienced average overwinter losses in excess of the15% economically sustainable threshold [1]. Honey bee colony mortality is most prevalent during the winter months in temperate climates, and, since 2007, Canadian beekeepers have experienced average overwinter losses in excess of the. In winter 2019, Canadian beekeepers experienced 25.7%. Pesticide exposure through stored honey and pollen is another potential stressor contributing to overwinter colony loss. Known as oilseed rape, is one of the most common bee-attractive crops grown in Canada, and most of this canola is grown from neonicotinoid-treated seed [2]. The neonicotinoid insecticides clothianidin (CLO) and thiamethoxam (THI) are commonly detected in pollen, nectar, and honey, at mean concentrations from 1.9–9.4 ng/g of CLO and 6.4–28.9 ng/g of Insects 2020, 11, 30; doi:10.3390/insects11010030 www.mdpi.com/journal/insects. In Saskatchewan, Canada, CLO was detected in 68% of honey samples at mean doses of
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