What’s killing the bumblebees? New study offers clues

bumblebee on a yellow flower Sandrinka/Shutterstock

Need another reason to give dandelions and bumblebees a break? British researchers say additives in the popular weedkiller Roundup may be harming pollinators, even when the active ingredient, glyphosate, does not.

Researchers at Royal Holloway, University of London sprayed bumblebees with four weedkillers commonly available in the UK. Three mixtures—two Roundup products and Weedol, a competitor—contain glyphosate, the world’s most common herbicide and one Health Canada says is “not expected to pose a risk” to pollinators. A fourth Roundup product was glyphosate-free. Bees were also sprayed with distilled water spray for a non-toxic comparison.

The results of the study found that the least harmful of the tested mixtures was Weedol, killing only four per cent of bees exposed. Most harmful was a glyphosate-free version of Roundup with 96 per cent mortality. It edged out the conventional glyphosate-equipped Roundup aimed at homeowners (94 per cent bee kill) and the product for farmers (30 per cent mortality.)

So if glyphosate—which is banned or restricted for domestic/cosmetic use in most provinces—isn’t the problem, what’s downing the bumblebees? Researchers Edward Straw, Edward Carpentier and Mark Brown point to surfactants—additives that help weedkillers coat plant leaves. Surfactants could be “spreading the formulation over the surface of the bumblebees, possibly limiting gas exchange” and smothering them. It’s difficult to know for sure, they add, because herbicide companies are not required to disclose all the ingredients in their mixtures.

For cottagers, “the best strategy is to reduce and eliminate the use of pesticides and herbicides,” says Vicki Wojick, director of the conservation group Pollinator Partnership Canada. Without knowing all the additives in a product and how they affect bees, she adds it’s difficult to pick a product that’s less harmful.

“What is absolutely crucial is you should not be applying any herbicide to a plant while it’s flowering” adds Susan Willis Chan, a University of Guelph post-doctoral researcher who has studied insecticide impacts on ground-nesting bees.

Here’s where the humble dandelion enters the story: they’re a key source of pollen and nectar for emerging bumblebees. “Every bumblebee you see in springtime is a queen,” adds Willis Chan. As the sole overwintering survivor of last year’s colony, the future rests on her success. “If she’s killed or hurt in some way, she will not be able to start a colony.”

Maybe it’s time to rebrand your dandelions. They’re not weeds—they’re your pollinator garden.

Read more: 7 ways you can help Canada’s bees


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