The gypsy cuckoo bumblebee is an assassin at risk.
The chubby, woolly parasitic bees hadn’t been spotted in Canada since 2006.
Many bee experts and entomologists assumed they were gone for good, until a surprising specimen was captured this summer near Stewart Crossing, by Yukon scientist and longtime bee champion Syd Cannings.
“It’s kind of hard to high five yourself, or else I would,” said Royal Saskatchewan Museum bee biologist and entomologist Cory Sheffield, who identified the gypsy cuckoo specimen. “Few people are aware of the status of these bees,” he said. “But when several species go from common to not common at all, we begin to wonder how this will affect us.”
The gypsy cuckoo - a freeloading bee that relies on other bumblebee species for its survival - is especially vulnerable. Most of the Yukon’s 23 bumblebee species start off in the spring with a single queen that lays enough eggs to build up a staff of worker bees - sterile females who gather pollen, tend to the queen’s ever-expanding cache of hatching eggs, and guard the colony. If the bees get chilly, they are able to detach their wings, flexing their wing muscles to warm themselves and their eggs. Come fall, the queen begins to hatch fertile females and males, who go on to mate with bees from other colonies. The fertilized females then seek out winter lodgings, burrowing into the soil or under compost piles. To stave of the frigid temperatures, the females buff up their blood with glycerol, a sugar alcohol compound that acts like antifreeze, allowing them to survive temperatures as low as minus 30 degrees.
Gypsy cuckoo bumblebees overwinter in much the same way, but come spring they don’t bother with the drudgery of colony building and egg-laying usually carried out by the queen. Instead the fat, fuzzy assassins wait until a queen has hatched a healthy, but not too healthy workforce, then sneak in for the kill.
It is a delicate balance. The gypsy cuckoo wants enough existing worker bees to care for its eggs, once it kills the queen and starts laying. But it doesn’t want a workforce strong enough to protect a queen against attack, putting it a risk. The gypsy cuckoo is also choosy about its colony. It is only known to infiltrate the nests of three species of bumblebee, the Western bumblebee, the yellow-banded bumblebee and the rusty-patched bumblebee. A decline in any of these host species means gypsy cuckoo populations, which rely on them, take a hit.
The Western bumblebee is one of several host species that began to decline rapidly in the mid-1990s, dropping off drastically across much of Canada and the US. No one is certain exactly what is taking a toll on the bees, though Sheffield suspects a combination of climate change, pesticide use, large-scale agriculture usurping natural food sources and urban sprawl are all playing a part.
“The status of our bee populations are warning flags for us,” he said. “Most of our crops are pollinated by bees, not to mention wild plants and berries, which feed wildlife, like bears - everything is affected.”
In northern areas, things aren’t so dire, yet. In fact, the Yukon’s Western bumblebee populations remain strong, despite declines across the rest of Canada and the US. “We wanted to look at the reason for that,” said Sheffield. “This led us to evaluate the species and we found the Western bumblebees in the North have molecular and morphological differences from the populations further south.” In other words, the Yukon’s Western bumblebees are genetically different from their southern counterparts, have different colour variations and are hairier.
Sheffield is unsure if these subtle genetic differences between northern and southern populations are playing a role in Western bumblebee survival rates. It is more likely that Yukon bees don’t face the same environmental stress as their southern counterparts, he said. There is less large-scale agriculture, less chemical use and less urbanization in the North. Sheffield also suspects there are fewer farmed bumblebee colonies.
In the south, greenhouse agriculture has been relying on commercially raised bumblebee colonies native to Ontario and Quebec to help with pollination. These bees, now being shipped across the country, may carry pathogens and parasites which could be spreading to wild bumblebee populations, said Sheffield.
For some bumblebees, pathogens and parasite levels are high, and may be affecting populations in the south, while northern bumblebees with the same high rates of parasites appear to remain unaffected for the time being. “It may be the cumulative impact of further stressors in the south, in addition to the parasites,” he said.
The drop in Western bumblebee populations across most of western Canada is mirrored in the gypsy cuckoo’s other host species, which are both at risk. The rusty-patched bumblebee may no longer exists in Canada at all, while the yellow-banded bumblebee is in dramatic decline in parts of its range. The gypsy cuckoo is already a delicate species, said Sheffield. “There have never been that many of them, because if there were, they would end up exterminating their hosts.”
The Yukon specimen is only the second gypsy cuckoo found in Canada in the past decade. “It still looks pretty bleak for this bee,” said Sheffield. “But because there is a healthy host community in the Yukon, they might be more abundant than we think.”
It will be another decade before this species is reviewed again. Resources and funding limit intensive monitoring for most species at risk. Sheffield, who is one of several members of the federal Committee on the Status of Endangered Wildlife in Canada, urges the public to help keep tabs on Canada’s bumblebees by taking pictures of the plump, hairy insects, documenting where and when they are spotted and posting the info and photos to the website Bumble Bee Watch, so scientists can identify the bees and add the sightings to their growing database. “There are 800 different species of bees in Canada, and for 750 of those species, we don’t have a lot of data,” he said. “We are hoping to get more data from parts of Canada where we wouldn’t have a lot of data otherwise.”
Bumblebees are among the champions of the bee world, said Sheffield. “They are major pollinators, and in the North you can see them flying in frigid temperature when other bees aren’t flying.” To help out the North’s fuzzy fliers, responsible for much of our food, Sheffield urges people to curb pesticide use and ensure there are lots of natural environments where native plant species can grow. “In the Yukon bumblebees are widespread and you’re not seeing the same declines as elsewhere in Canada,” he said. “So, ultimately, just keep doing what you’re doing.”
This column is co-ordinated by the Yukon Research Centre at Yukon College with major financial support from Environment Yukon and Yukon College. The articles are archived at http://www.yukoncollege.yk.ca/research/publications/newsletters-articles