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Combination of agricultural chemicals kills more bees than previously thought
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Combination of agricultural chemicals kills more bees than previously thought

  • Paul Rollings/CC BY 2.0

The combined effects of multiple agricultural chemicals, such as pesticides and herbicides, are having a greater impact on bee mortality than previously believed, according to a new study published Wednesday in the journal Nature.

The underestimations mean that bees are not protected by current regulatory processes, researchers warn.

Pollinators like bees are responsible for the successful reproduction of a majority of flowering plant species, meaning declining bee populations are a threat to food security and wild ecosystems worldwide.

Often, bees are exposed to pesticides and other chemicals by feeding on contaminated nectar and pollen which is collected in agricultural crops by foraging worker bees and then transported to the colony, according to a separate 2019 study also published in Nature.

In some cases, exposure to those chemicals during the larval phase reduced adult bees’ life spans and caused behavioral problems with adult bees, the 2019 study found.

What researchers found in Wednesday’s study was that chemicals had a synergistic effect — when two or more chemicals together are stronger than each by itself — on bee mortality, meaning more bees died when exposed to multiple chemicals.

“If you were to consider a honeybee colony, for example, if 10% of bees are killed by a chemical and another chemical kills another 10%, if those chemicals had a merely additive effect [as had been previously estimated], then, 20% of the bees would die,” said Harry Siviter, a researcher at the University of Texas at Austin. “What we found was that when bees were exposed to pesticides in combination, that the impact was synergistic — it was greater than that additive effect.”

Siviter and his colleagues also looked at other factors, such as parasites and a lack of nutritional sources due to habitat loss and how those stressors interact with each other and affect bee health.

Those stressors, however, are factors with which bees have co-evolved, and their accumulative effects were found to be no greater than additive expectations.

“Understanding the interactions between stressors is vital for pollinator conservation as it enables policy-makers to implement effective mitigation measures within the risk assessment process to reduce the negative consequences of anthropogenic stressors on bees,” researchers note.

With agricultural chemicals, it’s often the dose that makes it poisonous, Siviter said.

“So what you really want to have is you want to have a pesticide that does its job, but then disappears quickly. It's not persistence in the environment,” he said in an interview.

An even better solution, he added, would be “a move toward integrated pest management, where biological control and preventative measures and crop monitoring are promoted as a way of controlling pests, and then as an absolute last resort, if there's a pest outbreak, you can then use pesticides if needed.”

If the issue with agricultural chemicals is not addressed, researchers warn, it is risking a further decline in bee populations, which will lead to negative effects on pollination — “an invaluable asset to global food production."

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