One of the bumblebees that was most common in Southern Ontario when today’s baby boomers were teenagers has all but disappeared, a York University study has found.
The study provides the first quantitative evidence of the decline of bumblebees in North America by comparing recent bumblebee numbers with statistics gathered in the early 1970s in Ontario. It also tracks the dramatic decline of one species that is native to eastern Canada (including Ontario) and many American states.
The article “Evidence for decline in eastern North American bumblebees, with special focus on Bombus affinis Cresson,” appears online in the journal Biodiversity and Conservation. Its findings 
are disturbing because the loss of any pollinating species can have cascading effects on native plants and crops, and on anything that relies on them.
Lead author Sheila Colla (right), a PhD candidate in York University’s Department of Biology, studied the number and types of bumblebees at two sites in southern Ontario over three summers from 2004 to 2006, and compared them with baseline numbers from surveys at the same sites in the early 1970s. Colla slowly paced one kilometre across the sites at regular intervals, collecting all male and worker bumblebees as they foraged for pollen and nectar.
There were fewer bumblebees overall at the two sites – in southern Guelph and the town of Belwood – and half of the 14 species found in the 1970s were either missing or in decline. When Colla looked further afield and focused in on one species of bumblebee, she found the Bombus affinis had been nearly eliminated, not only in southern Ontario but throughout its native range.
“I found only one of the Bombus affinis species – one single bumblebee – at Pinery Provincial Park on Lake Huron, and I had looked for it at 43 sites from Ontario to Georgia, and east to Boston,” said Colla. “This is alarming because it appears to have been almost eliminated, and in the early 1970s it was one of the top four bumblebee species in southern Ontario.”
Each species has its own preferred flowers and its own season, says Colla. “Bombus affinis appears early in April, while other bee species make their first appearances in June. So if you knock one species out, there may be a few weeks where there are no bees pollinating some plant species.”
Left: A bumblebee
Colla’s research is one of a number of projects supervised by York Professor Laurence Packer, a world authority on bees and co-author of the study. Bees and bumblebees are vulnerable to extinction for many reasons – including pesticide use and lack of habitat – but there have not been many extensive surveys in North America, despite their ecological and economic importance as pollinators. Colla’s results are similar to patterns observed in Europe where bumblebees have been more closely monitored and half of all bumblebee species have been shown to be in decline.