Gardeners who are popping colourful annuals into their gardens as the nice weather arrives may want to take a moment to think about the birds and the bees.
Bumblebees appear to be in severe decline in southern Ontario, according to York University researcher Sheila Colla, and many of the annual plants that are so popular in city and suburban gardens are not suitable for them. In contrast, most native plants are suitable for many types of 
bumblebees and also produce seeds for birds.
This matters even more, according to Colla, a PhD candidate in York University's Department of Biology, because southern Ontario traditionally has been a hotspot for diversity of bumblebees.
Right: Sheila Colla in the field
"When people look in their gardens now, they may see a lot of bumblebees, but most of the time it is all one species. Thirty years ago there would have been a dozen species," says Colla. "In England, a large number of bumblebee species have either gone extinct or are endangered."
The dramatic losses of colonies of European honey bees in the United States and Canada recently – so-called "managed bees" that are brought in to pollinate crops – makes it even more important to encourage diversity by providing food and habitat for bumblebees, she says.
Colla spent three summers researching which bumblebee species in eastern North America are in decline and which are growing, comparing her findings with surveys performed from 1971 to 1973. There were 14 bumblebee species collected in Guelph and Belwood, Ontario, in the early 1970s, compared to only 11 collected by Colla at the same sites between 2004 and 2006. Three species had disappeared completely, five of the remaining 11 were declining in number, and two species had shot up dramatically in number – including Bombus impatiens, the bumblebees we now so often see in our gardens.
The species that was fourth-most-common in the 1970s – Bombus affinis – seemed to be missing, so Colla went looking for it.
Right: A bumblebee investigates the delights of Sea Holly. Photo by Lee Kindness.
"At the 45 sites I went to, all through eastern North America, I only found one individual, at Pinery Provincial Park on Lake Huron. I went south to Georgia, east to Boston, travelled all summer looking for it and I saw only one male," says Colla. "In the 1970s, if you collected a sample of bees, 14 per cent of what you collected would have been this species. So it's been hit hard and we don't know why."
Fruit and vegetable plants such as tomatoes and raspberries, wild roses, echinacea and other native flowers provide a steady supply of food for bumblebee colonies, which will die out in two or three days if the supply is interrupted at any point between the end of April and October, says Colla. Bumblebees also require habitat for nests, in cavities in logs, bare patches between flowers, and old rodent nests, so leaving backyards a little less than perfect helps the bees.
Research such as Colla's, which documents biodiversity, is one of the major focuses of the bee lab led by Professor Laurence Packer in York's Department of Biology, Faculty of Science & Engineering. A world expert on bees, Packer and his students have amassed a collection of more than 80,000 bees and are databasing information that will be used internationally to document bee diversity.
Packer is collaborating with scientists at 17 other institutions as part of the Canadian University Biodiversity Consortium (led by the University of Montreal) to create a networked database of all biodiversity-related information held in Canadian institutions.
He recently received more than $300,000 from the Ontario Research Fund's research infrastructure program to purchase cameras that will take series of pictures of bees at different planes of focus, and computers able to merge these pictures into almost three-dimensional computer images. The resulting images will be so detailed that scientists on the other side of the world should be able to identify even the tiniest species of bee by matching them to the images.