WASHINGTON Disease spread to wild bees from
commercially bred bees used for pollination in agriculture
greenhouses may be playing a role in the mysterious decline in
North American bee populations, researchers said on Tuesday.
Bees pollinate numerous crops, and scientists have been
expressing alarm over their falling numbers in recent years in
North America. Experts warn the bee disappearance eventually
could harm agriculture and the food supply.
Scientists have been struggling to understand the recent
decline in various bee populations in North America. For
example, a virus brought from Australia has been implicated in
massive honeybee deaths last year.
Canadian researchers 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
The researchers first observed that the commercial
bumblebees regularly flew in and out of vents in the sides of
the greenhouses, escaping from the facilities.
The researchers 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.
The model also predicted a drop-off in infection rates as
you get further from the greenhouses.
GREENHOUSE BUMBLEBEE PARASITES
The researchers 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 patterns that had been predicted by their mathematical
model were borne out by studying the wild bees, they said.
Most of the parasites in the wild bumblebees 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.
The researchers found that up to half of wild bumblebees
near the greenhouses were infected with this parasite.
"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.
"It was quite obvious that this was coming from the
greenhouses and it was a general adverse effect on the
bumblebees," Otterstatter added in a telephone interview.
He said the parasite weakens and often kills bees. The
"spillover" of disease from commercial colonies may be a factor
in the decline of bee populations in North America, he added.
The study, published in the Public Library of Science
journal PLoS ONE, can be read here
(Editing by Maggie Fox and Sandra Maler