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The trouble with bees

Bumblebee feeding on pollen from a yellow flower

Bumblebee (Bombus terrestris) feeding on pollen from a yellow flower. Source: Getty Images

The plight of bees has so much buzz it has reached the kitchen table. In mid-March, General Mills temporarily removed its bee mascot from the package of Honey Nut Cheerios to draw the attention to their dwindling numbers worldwide because of disease, pesticides and habitat loss.

Groundbreaking evidence from environmental science professor Nigel Raine, Rebanks Family Chair in Pollinator Conservation at the University of Guelph, shows the bee problem may actually be worse than we thought. In a study published in late 2015, in the scientific journal Nature, Raine produced the first evidence that low levels of the most commonly used group of insecticides impact the pollination services bumblebees provide to apples, more than 75 million tonnes of which are harvested every year by 95 countries.

At the doses at which they are used in the field, pesticides may not kill bees, but Raine and his team showed that typical levels of neonicotinoid pesticides affect bees’ ability to pollinate apple trees. Specifically, exposed bees visited apple trees and collected pollen less often.

So, what’s the big deal?

“Obviously, food is a major reason we should be worried about pollination services, and with global declines we will not have enough pollinators,” says Raine. “Our dependence on pollinator-dependent crops is increasing in the first world.”

In previous research, scientists, including Raine, discovered that the same group of neonicotinoid pesticides had an impact on the behaviour of bees, including their learning ability, foraging behaviour and reproduction. For Raine, the next step was to look further into what that meant. Says Raine: “If we’re seeing impacts on the behaviour of bees, are we seeing impacts on what ecosystem services they provide?”

“Food is a major reason we should be worried about pollination services, and with global declines we will not have enough pollinators”

For his latest study, Raine had three treatment groups of eight colonies each: one group received 2.4 parts per billion of the pesticide thiamethoxam in a sucrose solution over a two-week period; a second group received 10 ppb and a third group was untreated. The colonies were then released in flight cages that contained two varieties of potted apple trees, Scrumptious and Everest.

What he found was the bees collected less pollen the more insecticide they had been exposed to. That finding wasn’t all that surprising to the researcher. But he also found the more exposed bees were also less effective at collecting pollen. “That’s really, really important,” Raine says. “[Pollen] is a protein and lipid source for producing more bees. Larvae are basically built on that stuff.”

The researcher also noted a significant reduction in apple seeds — also a critical finding, Raine says. “From a crop production point of view, we know the number of seeds in apples is typically related to fruit quality. From a wider perspective, seed production in most wild plants is much more closely related to reproductive output.” In other words, the effectiveness of bumblebees as pollen transporters has important ramifications in terms of the future sustainability of crops and any other plants dependent on pollinators.

Ontario takes action

Until recently, farmers in Ontario have used neonicotinoid seed treatments on almost all of the corn and the majority of soybean seeds — the two top acreage crops grown in the province. Many experts believe this has contributed to the demise of bees and other pollinators. A big concern, Raine explains, is around the mobility of the pesticides. Neonicotinoids are typically applied as a seed treatment. Bits and dust from seed coatings and other pesticide residues can travel on the wind some distance from the field being planted. This may result in direct toxic effects to bees (and other pollinators) exposed to high appreciable levels of pesticide in the dust, or indirect effects as the active ingredient is taken up by flowering plants attractive to bees — wild flowers, for example — outside the treated fields. Even neonicotinoids that stay in the planted field don’t necessarily end up in the crop. Published information indicates that only 2 to 20 per cent of the active pesticide ingredient applied to the treated seed is taken up by the crop plant, meaning most of the rest ends up in the soil or water of planted fields.

This year, however, corn and soy growers in Ontario have been restricted as to when they can use neonicotinoids; half their crops must be free of the chemicals, and the province is aiming for 80 per cent reduction in cropland treated with these pesticides by 2017. Farmers are challenging the move in court.

And what about the bees?

Raine’s research has implications not just for crop production, but for the entire ecosystem. And for the bees? His findings are another chapter in a bad-news story. “It’s not just about pesticides,” says Raine. “It’s important to see the bigger picture. If they don’t have the base level of habitat or the flowers they need to feed on, then the other things are of less importance because the bees aren’t there anyway.”

More on this topic

Neonicotinoid pesticide exposure impairs crop pollination services provided by bumblebees

Pesticide Exposure Impairs Bumblebee Crop Pollination

Bee Expert Nigel Raine Studies the Plight of Pollinators

Current Biology: Nigel Raine

Exposure of bees to neonics linked to poor apple crops