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ARS researchers are
figuring out how to best protect alfalfa leafcutting bees from chalkbrood
disease. Click the image for more information about it. |
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Compound Safely Quells Bee-Killing
Chalkbrood
By Marcia Wood February 21, 2008
From rabbits to horses to cows, many animals love alfalfa. America's
premier pollinator of that crop, the alfalfa leafcutting bee (Megachile
rotundata), is vulnerable to a deadly fungal disease called chalkbrood. But
the bees might be best protected from chalkbrood if their leafy nests are
sprayed with an iprodione fungicide, according to Agricultural Research Service
(ARS) entomologist
Rosalind
R. James.
Caused by the Ascosphaera aggregata fungus, chalkbrood kills
bees while they're larvaewormlike young that hatch from eggs laid in
nests by female bees.
Healthy larvae spin cocoons within those nests, and later emerge as
young bees.
But chalkbrood-infected larvae may die before cocooning, according to
James. She leads the
ARS
Pollinating Insect Biology, Management and Systematics Research Unit in
Logan, Utah.
Microscopic spheres, called fungal spores, on dead larvae serve as
potent reservoirs of the disease. A healthy female alfalfa leafcutting bee
mayafter emerging from her cocoon and nest in springinadvertently
pick up some of those spores. If she spreads them to nests that she makes for
her eggs, she may doom her young.
James worked with alfalfa seedgrowers in Washington to determine how
to best protect alfalfa leafcutting bees from chalkbrood. The disease is so
pervasive in the United States that these seedgrowers buy at least 50 percent
of their alfalfa leafcutting bees each year from Canada, where chalkbrood is
less prevalent.
In experiments, James sprayed an iprodione fungicide on the
leafcutting bees' nests in spring, shortly before the adult bees left their
cocoons and nests. The treatment reduced the incidence of chalkbrood in the
bees' next generation by up to 50 percent, with no measurable loss of young,
James reported.
Now, James and her colleagues are looking for fungicides that may be
even more effective.
The research is part of ongoing studies to discover more ways to
safeguard wild bees, so they can help America's harried honey bees with
pollination chores.
Read
more about this research in the February 2008 issue of Agricultural
Research magazine.
ARS is the U.S. Department of
Agriculture's chief scientific research agency.