Scientists in the ARS Beneficial
Insects Research Unit at Weslaco,
Texas, have found that a strain
of the fungus Metarhizium anisopliae
is deadly to Varroa mites, such as
this one on an adult worker honey
Parasites known as Varroa mites infest honey bee colonies, sucking
blood from the bees and causing weight loss, deformities, diseases,
and reduced lifespan. These mites, which can nearly destroy an entire
colony within a few months, now infest honey bee colonies across most
of North America.
The honey bee is critical to maintaining natural vegetation, transferring
pollen between flowers as it collects the pollen and nectar for its
hive. And more than 130 agricultural plants in the United States are
pollinated by honey bees. Every year, beekeepers send their best bees
throughout the country to help pollinate crops, one farm at a time.
In 2003, the value they added to U.S. crops was estimated at $10 billion,
not including the honey, beeswax, and royal jelly also produced. USDA's
National Agricultural Statistics Service reported more than 2.5 million
honey bee coloniesup 1 percent from 2002and U.S. honey production
increased 5 percent, to 181 million pounds.
Since 2000, scientists in the ARS
Beneficial Insects Research Unit (BIRU) at Weslaco, Texas, have been
looking for a disease-causing agent, or pathogen, that can stop Varroa
mites. The mite has developed resistance to the only approved chemicalsfluvalinate
and coumaphosnow used for control, and coumaphos is on the U.S.
Environmental Protection Agency's "hit list" for possible
removal from the market. So the researchers have looked at various disease
agents, tried different dosages and application methods, and conducted
toxicity tests. Finally, they selected a strain of the fungus Metarhizium
anisopliae that was highly pathogenic to Varroa mites.
This potent fungus, which also kills termites, doesn't harm bees or
affect their queen's production. To test it, the scientists coated plastic
strips with dry fungal spores and placed them inside the hives. Since
bees naturally attack anything entering their hives, they tried to chew
up the strips, spreading the spores throughout the colony.
In field trials, once the strips were inside the hives, several bees
quickly made contact with the spores. Within 5 to 10 minutes, all the
bees in the hive were exposed to the fungus, and most of the mites on
them died within 3 to 5 days. The fungus provided excellent control
of Varroa without impeding colony development or population size.
"We tried to find a pathogen of Varroa, and we did it!"
says ARS entomologist Walker A. Jones, research leader of the BIRU.
Tests showed that Metarhizium was as effective as fluvalinate,
even 42 days after application. "Commercial beekeepers are very
edgy about using fluvalinate and coumaphos and are eager to see this
natural control get to market," Jones says.
This research was begun by Rosalind James, formerly with the Weslaco
unit. Lambert H.B. Kanga, former BIRU research associate and now chair
of the Entomology Department at Florida A&M University at Tallahassee,
continues to collaborate on the project. "While Metarhizium
doesn't kill as fast as fluvalinate and coumaphos, the result is the
same," Kanga says. "Metarhizium gets the job done,
and we won't have to worry about Varroa becoming resistant to
The scientific team is now fine-tuning the strategy for transfer to
Flores, Agricultural Research Service Information Staff.
This research is part of Crop Production, an ARS National Program
(#305) described on the World Wide Web at www.nps.ars.usda.gov.
Walker A. Jones
is in the USDA-ARS Beneficial
Insects Research Unit, 2413 E. Highway 83, Weslaco, TX 78596; phone
(956) 969-4852, fax (956) 969-4888.
"Saving Bees: Fungus Found To Attack Varroa Mites"
was published in the October
2004 issue of Agricultural Research magazine.