Researchers Develop Theory On Declining Bee Population
Researchers said on Tuesday it was possible that the mysterious decline in North American bee populations could be due to disease spread to wild bees from commercially bred bees used for pollination in agriculture greenhouses.
Scientists have been expressing alarm over the falling numbers of bee populations in recent years in North America. Experts warn the bee disappearance eventually could harm agriculture and the food supply.
The recent decline in various bee populations in North America has continued to baffle scientists. Last year, a virus brought from Australia was implicated in massive honeybee deaths.
Researchers in Canada studied another type of bee, the bumblebee, near two large greenhouse operations in southern Ontario where commercially reared pollination bees are used in the growing of crops such as tomatoes, bell peppers and cucumbers.
The commercial bumblebees regularly flew in and out of vents in the sides of the greenhouses, escaping from the facilities, the researchers noted.
They then devised a mathematical model to predict how disease might spread from this "spillover" of runaway commercial bees to their wild cousins.
The model predicted a relatively slow build-up of infection in nearby wild bumblebee populations over weeks or months culminating in a burst of transmission generating an epidemic wave that could affect nearly all of wild bees exposed.
It also predicted a drop-off in infection rates as you get further from the greenhouses.
They then sampled wild bumblebee populations around the greenhouses, catching bees in butterfly nets, holding them in vials and taking them back to a laboratory to screen for pathogens, including testing their feces.
The researchers acknowledged patterns that had been predicted by their mathematical model were borne out by studying the wild bees.
The wild bumblebees parasites were found to be at normal levels except for one intestinal parasite known as Crithidia bombi that is common in commercial bee colonies but typically absent in wild bumblebees.
Up to half of the wild bumblebees near the greenhouses were infected with this parasite, researchers said.
"All of the different species of bumblebees that we sampled around greenhouses showed the same pattern: really high levels of infection near greenhouses and then declining levels of infection as you moved out," said Michael Otterstatter of the University of Toronto, one of the researchers.
He added: "It was quite obvious that this was coming from the greenhouses and it was a general adverse effect on the bumblebees."
The "spillover" of disease from commercial colonies may be a factor in the decline of bee populations in North America, as the parasite weakens and often kills bees.
The researcher’s study was published in the Public Library of Science journal PLoS ONE.
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