As recently as the 1980s, the rusty-patched bumblebee was one of the most common bumblebees in Ontario, accounting for 15 per cent of all species. Then it virtually disappeared, to be spotted only once every five years or so, when a male strayed from the hive in search of food. Nobody knows what happened — not even Sheila Colla, a York University researcher who’s dedicated her career to studying the bee, and who was the last to record an Ontario sighting in 2009.
“The problem with studying rare species is if you only see one every five years, you don't really get to study why it's declining,” Colla says. “You can't watch it happening.”
There are a few possible reasons why the rusty-patched bumblebee is nearly extinct, but the speed of its decline, plus the fact that the insects disappeared even in regions untouched by development, suggest that a disease outbreak — perhaps caused by the fungus Nosema bombi — might have been the culprit.
Bees are incredibly diverse. There are more than 3,600 native species in North America. (The honeybee, although it gets the most ink, is not actually one of them.) All play a critical role in plant pollination.
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Sarah Johnson, lead biologist of Wildlife Preservation Canada's pollinator program, is developing captive breeding techniques with the yellow-banded bumblebee, a species that’s of special concern, meaning it’s at risk of becoming endangered or threatened. She hopes to apply her research to the rusty-patched bumblebee, if a colony is ever found.
“When the pollinator program was founded, the intention was to start a captive breeding program for the rusty patch — but the program was founded in 2013, so we couldn't find any,” Johnson says. “What we ended up doing was shifting our focus to a closely related species which is the yellow-banded bumblebee.”
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Locating the rusty-patched bumblebee is a big part of the problem for researchers looking to replenish the population with captive-bred specimens. There could be small pockets of them in the wild that haven’t been spotted. That’s why researchers developed Bumble Bee Watch, a citizen science website to track North American bumblebees. Having thousands of eyes out looking for the insect increases the chances of finding it.
“The first couple years we had [the website] running, we got more sightings of the rusty-patched bumblebee in the U.S. than before,” says Colla. “We're trying to build that up. Maybe we'll find some population, some remote place near Ottawa that hasn't been surveyed.”
Without finding a hidden population, the prognosis for the rusty-patched bumblebee is dire. Even if whatever killed them off were eliminated, there are so few bees left that it’d be difficult to find enough queens to restore the species through captive breeding.
But Johnson’s work is helping to conserve Ontario’s other bee species, partly by raising the alarm for them. If one as numerous as the rusty-patched bumblebee can disappear so quickly, then it’s likely others are equally vulnerable — and researchers can guard against similar downfalls in the future by analyzing possible causes for the rusty-patched bumblebee’s decline.
The rusty-patched bumblebee may never be abundant in Ontario again, but it will always serve as a warning about what can be lost when we’re not watching.
“Because it was so drastic, now we can have our guard up for other species,” Colla says.