Pesticides may threaten spring breeding of wild bees, researcher says

A new international study suggests thiamethoxam, one of the most commonly used neonicotinoid pesticides, is disrupting the reproductive health of wild bumblebees. 

The chemical is widely used to coat crop seeds prior to planting so that when they germinate, the insecticde is carried throughout the plant's vascular system, thereby inoculating it against insect pests while also exposing pollinators through the plant's pollen. 

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Nigel Raine, a professor in the school of environmental studies at the University of Guelph, was among a team of international researchers who wanted to examine the possible effects of exposure to the chemical on wild bumblebees during the spring planting season, a crucial time in the insects' reproductive health. 

"When the queens have just emerged and they are trying to set up a colony, they are effectively carrying the hopes of their colony going forward," Raine told CBC Kitchener-Waterloo's The Morning Edition host Craig Norris Thursday.

Bees carried smaller eggs

The researchers went into the field and collected four different species of wild bumblebees that were foraging on canola or oil seed flowers in the U.K.

They then gave some of the insects two doses of thiamethoxam, which would have been the equivalent of what they would have been exposed to during the spring plant, while a control group was not exposed to the pesticide.

The scientists then monitored the rate at which the insects fed on artificial nectar as well as the development of their ovaries. 

About one in three mouthfuls of food we eat are dependent on the unmanaged pollination services of wild bees. So we would see a significantly harder job for farmers to produce that food.- Nigel Raine, University of Guelph researcher

"What we found was that in all four of the species, at the higher level of neonicotinoid exposure that the size of the eggs in their ovaries was significantly smaller, which we think means probably that they would lay their eggs later and their colonies would develop and start later than those who were not exposed to the pesticide," Raine said.  

"In two of the four species we also found a reduction in the amount of the nectar they were eating, which is going to limit the amount of energy they have for flying around to find food and to look after the offspring, to look after the eggs and larvae once they've laid them."

Wild bees key to agriculture

The study suggests exposure to the chemical during the spring planting season seems to have a disruptive effect on the breeding cycle of wild bumblebee, which could lead to a decline in their numbers. 

Raine said that wild pollinators, such as bumblebees, are vital to farmers work and play a large role in delivering abundant harvests of fruits and vegetables. 

"About one in three mouthfuls of food we eat are dependent on the unmanaged pollination services of wild bees," he said. "So we would see a significantly harder job for farmers to produce that food and presumably a rise in food prices or a shortage in those foods if we lose pollinators."

Raine also noted the repercussions would likely go much further than agriculture. 

"About 90 per cent of flowering plant species rely on some form of animal to pollinate them and bees are really important pollinators," he said.

"So losing wild bees would significantly change our landscapes and change our ecosystems."