Some queen bumblebees exposed to a common insecticide may never lay eggs or start colonies, which would lead to their extinction, researchers say.
The latest findings, published Monday in the journal Nature Ecology and Evolution, found exposure to thiamethoxam can substantially affect how many eggs are laid by queen bees.
A year ago, the same Canadian and British researchers showed queen bees were less likely to feed, and their eggs developed more slowly after just a two-week exposure to thiamethoxam, an insecticide in the neonicotinoid family.
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The tests examined exposure amounts that would be similar to those sprayed on a farmers' field. Bumblebees are important crop pollinators.
'Could go extinct'
Queen bees exposed to thiamethoxam for two weeks were 26 per cent less likely to lay eggs, the research shows. No eggs means no worker bees, which means no new colonies.
"A reduction this big in the ability of queens to start new colonies significantly increases the chances that wild populations could go extinct," said Nigel Raine, the Rebanks Family Chair in pollinator conservation and a professor at the University of Guelph in Ontario.
Raine conducted the study with Dr. Gemma Baron and other researchers from Royal Holloway, University of London.
"Creating new bee colonies is vital for the survival of bumblebees — if queens don't produce eggs or start new colonies, it is possible that bumblebees could die out completely," Baron said.
Spring queens represent next generation
The researchers focused their research on spring queens, because they play a vital role in maintaining bumblebee populations.
"The spring queens represent the next generation of bumblebee colonies," Raine said.
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More than 300 queen bees were exposed to environmental stresses common in the field, including parasite infections. About half of the queen bees survived hibernation, and those that did were then fed a syrup treated with pesticide for two weeks. The amount of insecticide was similar to that found in wild pollen and nectar.
The researchers then observed the bees for 10 weeks and recorded egg-laying behaviour and mortality rates.
Vincent Jansen, a Royal Holloway, University of London professor, said the mathematical models used showed "a very real threat to the survival of wild bumblebee populations."
'If queens don't produce eggs or start new colonies, it is possible that bumblebees could die out completely.' - Dr. Gemma Baron
"Neonicotinoids are the most widely used class of pesticide in the world," he said. "It is vital that we understand the effects of these pesticides on our wildlife before allowing their continued use."
The results should be a concern for policymakers, in helping achieve "population sustainability" and avoid extinction, they wrote in the study.
Policies relating to the use of neonicotinoids should take into consideration factors such as when and how these compounds are applied, and the life-cycle stages of bees, the researchers recommend.