Climate change amplifies pesticide effects on bees, threatening pollination services

A recent study conducted by researchers at Imperial College London has revealed that temperature plays a crucial role in determining the impact of pesticides on bee behavior. The study suggests that climate change-induced extreme temperature events in the future could exacerbate the effects of pesticides on bee populations and their ability to provide pollination services.

Neonicotinoids, a specific class of pesticides, have been known to negatively affect bees and other vital insects, potentially contributing to declines in their populations. However, the responses of bees to this pesticide threat have been observed to vary across different regions worldwide, indicating the presence of other influencing factors.

The researchers at Imperial College London have now demonstrated that the environmental temperature can modulate the extent to which pesticides alter various behaviors crucial for the survival and pollination capabilities of bumblebees. The findings of this study were published today in the journal Global Change Biology.

Pesticide effects on flight under heat waves

In their study, the research team examined the impact of two pesticides, imidacloprid (a neonicotinoid) and sulfoxaflor (a sulfoximine), on six specific behaviors of bumblebees. These behaviors were studied at three different temperatures: 21°C, 27°C, and 30°C.

The results revealed that four of the behaviors – responsiveness, likelihood of movement, walking rate, and food consumption rate – were more strongly affected by imidacloprid at the lower temperature. This implies that cold temperatures could enhance the toxicity of pesticides on behaviors crucial for nest-related activities.

However, the most significant effect of imidacloprid was observed on a key behavior – the flight distance of the bees – at the highest temperature. The relationship between imidacloprid exposure and flight distance exhibited a substantial decline, with no significant difference between 21°C and 27°C, but a sharp decrease at 30°C.

Dr. Richard Gill, the lead researcher from the Department of Life Sciences at Imperial, noted that the decline in flight performance at the highest temperature indicates a potential “tipping point” where the bees’ tolerance to the combined effects of temperature and pesticide exposure is surpassed. This drop in performance occurs within a narrow temperature range of just three degrees, challenging our understanding of pesticide risk dynamics considering that such temperature changes can occur within a single day.

Furthermore, the study highlights the projected increase in pesticide and extreme temperature exposure frequencies for bees under climate change. The findings can assist in determining the appropriate pesticide concentrations and application timings in different climatic regions worldwide, aiming to safeguard crucial pollinators like bees.

Pollination problems

The ability of bees to fly long distances is vital for their role in pollinating crops, ensuring food security and supporting agricultural diversity. While tropical regions generally experience higher temperatures, it is plausible that pollinator populations in temperate latitudes, including the UK, might be more susceptible to pesticide effects due to larger temperature variations.

Bees play a crucial role in pollinating various crops such as cereals, legumes, and fruit trees. As our food production becomes more diversified, the demand for bee pollination services will increase. However, this also means that bees will face additional challenges from climate change and the intensification of insecticide use.

The findings of this study, which establish the relationship between temperature and pesticide impacts, can contribute to modeling the risks associated with pesticides in different regions as the climate continues to shift. Daniel Kenna, the first author of the study, emphasizes the significance of considering environmental context when assessing pesticide toxicity, particularly when predicting how bees will respond to future climate change.

Dr. Peter Graystock, a co-author of the study, highlights the importance of these results in developing a framework for predicting the toxicity of pesticides and understanding how bee populations will cope with climate change within highly agricultural landscapes.

Moving forward, the research team aims to conduct more comprehensive studies across a wider temperature gradient to determine how the effects of pesticide toxicity scale with temperature and identify specific tipping points for various bee species.

Source: Imperial College London

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