With a tenth of US and Canadian bumblebee species under threat, researchers are drawing up a plan of action. Credit: Thom Wilson

In a bid to curb the rapid decline in 10% of wild North American bumblebee species, international researchers have agreed on the key scientific priorities that will drive the next steps — including the establishment of a body to push forward research.

The United States and Canada are home to about 50 species of native bumblebees (genus Bombus), which are important wild pollinators of fruit and vegetable crops. Several species have been domesticated and used for commercial pollination in tomato greenhouses. Honeybees tend to perform poorly in tomato pollination.

But in the last three years, researchers have identified five North American species that have undergone a relatively swift population reduction since the 1990s, says Sydney Cameron, an evolutionary biologist at the University of Illinois in Urbana-Champaign. For example, the Bombus franklini worker bee was widespread in northern California and southern Oregon in 1998, but scientists conducting surveys in 2007 found only one, she says.

Three species — B. affinis, B. terricola, and B. occidentalis — will be submitted to the International Union for Conservation of Nature (IUCN) Red List of Threatened Species after a conference held at the Saint Louis Zoo in Missouri on 9-12 November. The conference brought together researchers, government agencies and commercial breeders to set future research priorities that might help to stem declines in bumblebee numbers.

Bee killer

The delegates drew up a shortlist of research priorities, such as finding the cause of the bumblebee disease thought to be behind the population crashes. Some researchers have pinned the die-off of native bumblebees on a fungal pathogen, Nosema bombi, which could have been introduced into the United States when commercial bumblebees introduced into Europe by breeders then brought back escaped into the wild. A related parasite has been implicated in the well-known decline of honeybees, although the two events seem to be unconnected, says James Strange, an entomologist at the USDA-ARS Bee Biology and Systematics Laboratory in Logan, Utah, a conference organizer.

But commercial breeders at the meeting pointed out that the evidence implicating N. bombi was circumstantial and insufficient to establish any firm theories, says Ed Spevak, curator of invertebrates at the Saint Louis Zoo, who also helped organize the conference.

The researchers suggested organizing efforts to determine the pathogen's transmission rate and identify any other diseases possibly infecting the bumblebees.

Other attendees concentrated on climate-change impacts that could be exacerbating the decline. For instance, flowers may bloom one or two months early, says Spevak, which may mean queen bumblebees find less nectar when they come out of hibernation. This group proposed long-term monitoring projects and a better understanding of different species' life history to help counteract such problems.

Surveying the problem

In order to check the status of bumblebee populations across the United States, conference participants suggested gathering and digitizing information from databases of different agencies, such as the US Forest Service or Fish and Wildlife Service, says Cameron, also a conference organizer. The results should be coordinated and augmented with sightings in gardens made by members of the public, she says. Researchers already enlist help from garden clubs and nurseries to monitor these "islands of bee biodiversity", she adds.

Scientists at the conference also identified a need for basic research into bumblebee genetic diversity. Current evidence suggests that the declining species exhibit low genetic diversity and tests could determine additional species at risk of a future die-off.

Attendees also agreed on a proposal to create an IUCN bumblebee specialist group that can coordinate the necessary research that will help policy-makers counteract the population loss.

Although a great deal of research remains to be done, many are hopeful that work from the conference will start to stem the bumblebee's decline. "In a few days, we can't expect to resolve all these problems, but I think a lot of progress was made," says one conference attendee, Robbin Thorp, professor emeritus of entomology at the University of California, Davis.

Having representatives from government and industry in addition to researchers means the priorities discussed at the meeting stand a better chance of getting implemented, says Spevak.

"The only way to develop a good conservation plan is to have everyone feel like they're a part of it," he says. A final version of the draft strategy should be available early next year, Spevak adds.