Commercially Bred Bees Spread Disease to Wild Bees
US: July 24, 2008
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 cucumbers.
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 at http://www.plosone.org/doi/pone.0002771.
(Editing by Maggie Fox and Sandra Maler )
Story by Will Dunham
REUTERS NEWS SERVICE
|