The evidence linking bee deaths to a common agricultural bug killer is mounting, and now, a Canadian study has found that neonicotinoid pesticides also affects the abilities of still-living bees.

Bumblebees exposed to neonicotinoid pesticides become impaired and unable to support their colonies, causing those colonies to slowly die, according to the results of a study out of the University of Guelph.

The study, which was published Tuesday in the British Ecological Society’s journal Functional Ecology, tracked the foraging habits of 40 bumblebee colonies over four weeks. Researchers fitted the insects with tiny microchips to track their movements via radio and compared the habits of neonicotinoid-treated bees with untreated bees. The study found insects exposed to neonicotinoids fared significantly worse than their untreated counterparts.

“The bees treated with neonicotinoids were much less able to collect pollen,” University of Guelph researcher Nigel Raine told CTV’s Canada AM. “They actually became worse at collecting pollen, which is exactly the opposite of what you would expect.”

While most bumblebees learn from their pollen-gathering experience and become more efficient, Raine said the pesticide-treated bees actually grew worse at their jobs as time went on.

Neonicotinoids are chemicals used to treat corn and soybean seeds to protect the grown plants against harmful pests. Pesticide companies have repeatedly denied any link between neonicotinoids and a global decline of the bee population, despite recent studies that have concluded the link does exist.

A Harvard study released in May suggested neonicotinoids are likely the “main culprit” in bee deaths.

Behavioural impact

Raine said his study reinforces that link.

“There’s a body of evidence now which is suggesting that these neonicotinoid pesticides have a behavioural impact on bees,” he said.

Neonicotinoids have also been linked to colony collapse disorder, which occurs when honeybees become lost and unable to find their way back to the hive. Beekeepers often find the insects fallen mere steps from the hive entrance, dead from starvation. Eventually, the whole hive can die.

Most neonicotinoid studies have focused on honeybee populations housed in apiaries, but the Guelph study examined the honeybee’s larger, untamed cousin, the bumblebee.

The Ontario government recently became the first province in Canada to acknowledge the potential hazards of neonicotinoids, announcing Monday it will look into restricting the pesticide’s use. The province stopped short of agreeing to an indiscriminate ban, declaring instead that it will focus on a “balanced approach based on science,” according to a statement from Agriculture, Food and Affairs Minister Jeff Leal.

Over 95 per cent of corn fields and as much as 60 per cent of soybean fields in Ontario were planted with neonicotinoid-treated seed last year, according to the Ontario Bee Health Working Group Report. Since then, the Ontario government has pledged to make more non-treated seeds available to farmers, but supply remains a problem.

Neonicotinoid pesticide producers like Bayer have said the chemical is not responsible for bee deaths, and have pointed to the Varroa mite as a more likely culprit. Bayer has also launched its own bee health education centre to address neonicotinoid criticism. “While many laboratory studies described sub-lethal effects (of neonicotinoids), no adverse effects to bee colonies were ever observed in field studies at field-realistic exposure conditions,” the Bayer Bee Care site says.

The European Union is in the middle of a two-year temporary ban of the pesticide so it can study the bee population without neonicotinoid pesticides on crops.