A new study on bumblebees has found that exposure to pesticides reduces by one-quarter the chances that queen bees will start up a colony in spring, a result which could be having a “devastating effect” on wild bee populations, according to the researchers.
Declines in wild bee populations are becoming a worldwide concern, as their role in helping to pollinate plants and crops is coming under threat from a number of different angles. Habitat loss due to human development, parasites, invasive species and ecological changes brought about by climate change have all been identified as potential factors.
At the top of the list, however, is pesticide use, which studies have shown to have a negative impact on bee behaviour, reproduction and colony survival. Now, a new study on bumblebees shows that exposure to thiamethoxam, a commonly used neonicotinoid insecticide, caused a 26 per cent reduction in the proportion of queens that laid eggs. Researchers say that this one-quarter decline in colony founding “dramatically increases” the likelihood of population extinction.
Effective pollinators both for agricultural and natural plant species, the annual lifecycle for bumblebees sees solitary female queens initiating a colony each spring, a vulnerable time for a bee population, as the queen does not have a whole colony to help mitigate environmental stressors like pesticide exposure. Thus, gauging the impact of neonics on queens at this stage in the cycle is crucial, says Nigel Raine with the School of Environmental Sciences at the University of Guelph in Guelph, Ontario.
"These spring queens represent the next generation of bumblebee colonies,” says Raine, co-author of a new study published in the journal Nature Ecology & Evolution, in a press release.
“When a queen is going to set up a colony, she will secrete wax and form it into containers for nectar and pollen. She will then begin to lay her eggs and sit on them like a bird.”
Researchers working with more than 300 queen bumblebees fed them syrup treated with pesticides at levels similar to those found in wild pollen and nectar for two weeks and then recorded their egg-laying behaviour and mortality rates for ten weeks thereafter. The results showed a 26-per cent reduction in the queens’ egg laying, with the pesticide-treated queens also laying their eggs earlier than a control group of untreated queens.
“Pesticides cause metabolic changes in honeybees, including the regulation of genes associated with immune function and detoxification,” say the study’s authors. “It therefore seems likely that the shift in the timing of colony initiation observed in the current experiment was a response to physiological stress from pesticide exposure.”
A recent study from Michigan State University has found that another threat to bees, the Varroa mite, may be vulnerable to attack by a “genetic cocktail.” Providing a ray of hope for honeybee populations which have been decimated by the parasite, researchers identified four genes in Varroa mites that control reproduction and two genes that cause high mortality rates, one of which was found to kill more than 96 per cent of the mites.