A naturally derived pesticide previously considered safe for insect pollinators may hamper the foraging of wild bees, researchers report.
Bumblebee larvae raised on pollen spiked with spinosad, an insecticidal mixture of chemicals made by bacteria, grow up to be slow, clumsy foragers, say Lora Morandin of Simon Fraser University in Burnaby, British Columbia, and her colleagues in the July Pest Management Science. As adults, the bees suffer from muscle tremors and take longer to penetrate complex flower structures than do bees nourished as larvae with untainted pollen, the researchers found.
Previous studies on bees hadn’t focused on sublethal effects of pesticides or on larvae, says Morandin. Moreover, researchers had looked mostly at domesticated honeybee colonies, which farmers can move before spraying a field. Wild bee colonies don’t relocate during spraying, and so these bees probably suffer higher exposures to pesticides.
At least one-third of the food produced in developed countries relies on bees, birds, and other pollinators. Wild bees probably make a significant contribution, though their role hasn’t been quantified. In a forthcoming Ecological Applications, Morandin shows that canola plants in fields with large wild-bee populations produce more seeds than do plants in fields with fewer wild bees.
Mark Winston, also of Simon Fraser University and a coauthor of the pesticide study, notes that bees were affected by spinosad concentrations that insects might reasonably encounter in a crop field. Even so, he adds, the pesticide, which farmers use on many crops against a wide range of insects, shouldn’t necessarily be scrapped. Rather, he says, “timing, dose, and formulation may need to be managed in order to use this pesticide properly.”