OTTAWA -- Exposure to even small amounts of pesticides is preventing bumblebees from efficiently extracting pollen from their favourite wildflowers, says a new study, raising concerns that the chemicals are impairing the insects' ability to learn.
And scientists warn that could affect the ability of the bees to pollinate both crops and wild plants, which can ultimately harm the food supply.
The findings, contained in a study co-authored in Canada and the U.K., show that bumblebees exposed to a realistic level of a neonicotinoid insecticide called thiamethoxam, collected more pollen, but took longer to do so than control bees.
The study, published Monday in Functional Ecology, found that low exposure to the crop chemical can hinder the ability of bumblebees to develop the skills they need to collect nectar and pollen.
While several studies have been conducted on the effects of pesticides on the honeybee population, these findings are the first to explore how the chemicals may affect the ability of bumblebees to forage from common wildflowers.
The pesticides confuse the insects, changing their foraging behaviour and floral preferences and hindering the development of the skills needed to extract nectar and pollen, says University of Guelph professor and senior author Nigel Raine.
"Bees rely on learning to locate flowers, track their profitability and work out how best to efficiently extract nectar and pollen," said Raine.
"If exposure to low levels of pesticide affects their ability to learn, bees may struggle to collect food and impair the essential pollination services they provide to both crops and wild plants."
Deadly parasites and diseases have been blamed in part for contributing to a widespread collapse of bee populations in parts of the world.
But several studies have also shown that neonicotinoid pesticides can cause changes in the brains of honeybees, more specifically in the areas associated with learning and memory.
Raine said more research is needed into the impact of all pesticides on bumblebees and other wild pollinators.
The Ontario government unveiled restrictions on the use of neonicotinoid insecticides last year -- a first in North America -- after beekeepers lost more than half their hives in 2013-14.
Under the new rules, farmers cannot use seed treated with neonicotinoids on half their land this year, and on any of it in 2017, without crop and soil assessments proving they have crop-eating worm or insect infestations.
The rules also require seed vendors in the province be licensed to sell the three most commonly used neonicotinoids, although Ontario's environment minister conceded there is little to prevent anyone from purchasing the chemically-treated seeds in the United States.
While the chemicals have been banned in Europe, Ontario farmers are fighting the restrictions through the courts.
Quebec farmers have also complained about planned new guidelines in their province which, if successfully implemented, would require farmers to get permission from agronomists before using certain "high risk" pesticides on their crops.
Health Minister Jane Philpott announced in January that the federal government will end the rare practice of allowing the use of pesticides that aren't fully approved for sale, effective June 1.
But Ottawa has not specifically restricted the use of neonicotinoids.
Crop seeds are treated with neonicotinoids before they are planted. The chemical is then infused in the plant as it germinates and kills pests in the early growing stages.
But pesticide residue remains in the nectar and the pollen that bees and other pollinators feed on, and has also been found in crop dust after the plants are harvested.
