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Pesticide-dosed
bees can lose
royals, way home
By Susan Milius
What does not kill them does not in fact
make them stronger when it comes to
bees and pesticides. Two unusual studies with free-flying bumblebees and
honeybees find that survivable exposure
to certain pesticides can lead to delayed
downturns in bee royalty and a subtle
erosion of workforces.
Pesticides appear as a suspect in widespread declines, some subtle and some
striking, of bees and other animals that
pollinate crops and wild plants. And in
one of the most dramatic still-unsolved
mysteries in those declines — why honeybee colonies suddenly collapse — one
leading hypothesis combines chronic
pesticide exposure with other stressors
such as disease.
Both new studies, appearing online
March 29 in Science, test the risks of foraging on flowers treated with common
insect killers from the nicotine-related
class called neonicotinoids. These pesticides course through the whole plant,
killing aphids and a range of other nibbling and sipping pests, but also work
their way into the nectar and pollen that
bees collect.
To simulate pesticide exposures that
bumblebees might encounter when
a field of canola blooms, entomolo-gist Dave Goulson of the University of
Stirling in Scotland and his colleagues
fed 50 Bombus terrestris lab colonies nonfatal doses of the pesticide imidacloprid.
After two weeks of eating spiked pollen
and sugar water, bees were set outside
and allowed to forage around the Stirling
campus at will. By season’s end, the
pesticide-dosed colonies were an average
A great yellow bumblebee makes its
rounds. Low doses of pesticides caused
bumblebee colony sizes to drop and the
colonies to produce fewer queens.
of 8 percent to 12 percent smaller than
25 unexposed neighbor colonies.
More noticeably, the contaminated
colonies managed to produce only about
two young queens each. The other colonies averaged about 14. Pitiful production of new young queens bodes ill for
bumblebees because all other colony
members die at the end of the growing
season. Young queens represent each
group’s sole hope for making new colonies the next year.
A drop in pollinator reproduction is
the kind of finding that can get the attention of agencies regulating pesticide use,
says Jeffery Pettis, a U.S. Department of
Agriculture bee researcher in Beltsville,
Md. With these and previous studies,
concerns are growing that usage rules for
neonicotinoids may need to be tightened.
Goulson’s study ranks as the first in
bumblebees of pesticide side effects
under natural field conditions, says Guy
Smagghe of Ghent University in Belgium.
Smagghe also works with bumblebees,
which many wildflowers and crops such
as tomatoes and peppers depend on.
For honeybees, earlier tests have
raised the possibility that chronic, non-
fatal exposure to neonicotinoids impairs
learning, memory and other capacities
that bees need for good flower hunting.
To set up a test with bees flying freely
outdoors, a research team in France used
dental cement to fasten electronic iden-
tifiers onto more than 600 bees. Feeding
bees low doses of the pesticide thiameth-
oxam in sugar water provided a realistic
exposure, says coauthor Mickaël Henry
of the French National Institute for
Agricultural Research in Avignon.
