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Rising temperatures increase pesticide toxicity in bees

Some pesticides – particularly a class called neonicotinoids – are known to have a significant impact on bees and other insects, contributing to population declines. Yet, since bees’ responses to this threat across the globe often seems to vary, other factors might be at play. 

Now, a team of scientists from Imperial College London (ICL) has found that environmental temperature is one of these factors, influencing the degree to which pesticides alter a variety of bumblebee behaviors that are crucial for their survival and capacity to pollinate crops. These findings suggest that future global warming could increase the impact of pesticides in bee population and their pollination services.

The experts examined how six bumblebee behaviors were influenced by two widely used pesticides – the neonicotinoid imidacloprid and the sulfoximine sulfoxaflor – at three different temperatures (21, 27, and 30°C). The investigation revealed that four of these behaviors – responsiveness, likelihood of movement, walking rate, and food consumption rate – were affected by imidacloprid more strongly at lower temperatures, suggesting that cold snaps may increase pesticide toxicity on essential behaviors. However, a behavior highly important for pollination – how far the bees could fly – was most significantly affected by exposure to imidacloprid at the highest temperature.

“The drop-off in flight performance at the highest temperature suggests a ‘tipping point’ has been reached in the bees’ ability to tolerate the combined temperature and pesticide exposure. This seeming cliff-edge effect happens over the span of just three degrees, which changes our perception of pesticide risk dynamics given such temperature changes can commonly occur over the space of a day,” said study senior author Richard Gill, a senior lecturer in Life Sciences at ICL.

“Furthermore, the frequency to which bees will be exposed to pesticides and extreme temperatures under climate change are predicted to increase. Our work can help to inform the right concentrations and application times of pesticides across different climatic regions of the world to help safeguard pollinators, such as bees.”

The scientists stress that, although the tropics are hotter in general, since temperature ranges are larger in more temperate latitudes, pollinators may be affected more strongly in such regions. By quantifying the relationship between pollination services and pesticide impact, this study could play a significant role in assessing the risks of pesticides across different regions of the world as the climate continues to warm.

“These results are important for developing a toxicity forecast framework, allowing us to predict how bee populations will respond to climate change whilst living in intense agricultural landscapes,” concluded co-author Peter Graystock, an expert in Conservation Biology at ICL.

The study is published in the journal Global Change Biology.

By Andrei Ionescu, Staff Writer

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