Varroa-Tolerant Bees Keep Hives
Visible as a dark, oval shape, an adult female varroa mite feeds on the
midsection of a developing worker bee.
An eight-legged, blood-sucking
parasite known as the varroa mite ranks as one of the worst enemies of honey
bees worldwide. About one-sixteenth inch in size, Varroa jacobsoni mites
have attacked in nearly every state, killing bees needed for making honey and
for pollinating an estimated $8 to $10 billion worth of crops.
Varroa mites feed on the blood of adult bees and developing young bees that
are still soft, white pupae. Parasitized bees may have deformed wings and
abdomens and a shorter life span than their unparasitized hivemates. What's
more, varroa mites are thought to transmit at least a half-dozen bee viruses.
But honey bees that can tolerate attack by the mite may hold an important
key to stopping today's devastating losses to this parasite.
ARS geneticist Tom Rinderer (right foreground) and beekeeping cooperator Steve
Bernard, along with ARS associates Tony Stelzer and Warren Kelley (background,
L-R) of the Baton Rouge laboratory, inspect colonies of Russian and other honey
ARS entomologist Eric H. Erickson and
colleagues monitored mite infestations in research apiaries. The scientists
populated the apiaries with survivors from hives that had not been treated with
mite-controlling chemicals, or miticides.
"We rated a hive as varroa-tolerant if it had no more than 15 mites for
every 100 adult bees," says Erickson, who heads the ARS Carl Hayden Bee
Research Center in Tucson, Arizona. "Our experimental apiaries, which we
kept miticide-free, usually scored better than this, often having fewer than 7
mites per 100 bees."
Erickson says the 4-year experiment provides additional evidence that
beekeepers can produce and maintain varroa-tolerant strains from established
stocks of our domesticated honey bee, Apis mellifera.
"Some beekeepers and breeders already do this successfully," he
On Marsh Island, Louisiana, an
isolated ARS research facility used
for producing pure stocks of Russian
bees, technician Gary Delatte
prepares hives for transport.
Russians to the
Hardy honey bees from the mite-infested Primorski region of Russia's Far
East may also offer natural genetic resistance that could be bred into U.S.
"The Russian bees are the same species as our domesticated honey
bee," says ARS geneticist Thomas E. Rinderer. "But we suspect that,
over time, the constant mite challenge in that region led nature to favor
survival of only the most mite-resistant bees." Rinderer heads the ARS
Honey Bee Breeding, Genetics, and Physiology Research Unit in Baton Rouge,
In 1997, Rinderer brought some of the rugged Russian bees to an ARS
quarantine facility on small, sun-baked Grand Terre Island off the coast of
Louisiana. His studies there indicate that mite populations in some hives
deliberately infested with the parasite decreased as much as one third, while
mites in some research hives of domestic bees increased fivefold.
Beekeeping assistants Matt Wyble and Guy Foret and technician Gary Delatte
(L-R) unload colonies of Russian honey bees on Marsh Island to obtain pure
mated Russian queen bees. The island is far enough from land that no other
honey bees are present.
"If this resistance proves
constant," says Rinderer, "beekeepers may in some cases be able to
reduce, if not eliminate, miticide treatments by relying on the Russian
Rinderer has sent Russian bees to commercial bee colony suppliers in Iowa,
Mississippi, and Louisiana to evaluate the insects for temperament, honey
production, and pollination skillstraits beekeepers value. "If their
reports to us are good and mite resistance continues to be high," says
Rinderer, "the Russian bees could make their national debut next
Widespread use of a miticide called fluvalinate, or Apistan, has
"inadvertently contributed to the rise of mites resistant to this
chemical," says ARS environmental toxicologist Patti J. Elzen.
Recently, Elzen and colleagues in the ARS Beneficial Insects Research Unit
at Weslaco, Texas, found fluvalinate resistance in varroa mites collected from
California, Wisconsin, Arkansas, and Florida. Based in part on the Weslaco
research, Florida state officials this year were the first to seek and obtain a
1-year emergency exemption from the federal Environmental Protection Agency to
allow use of an alternative chemical, coumaphos.
Beekeeper Steve Bernard and ARS entomologist Lilia de Guzman extract developing
bees from a comb to check for mites.
Coumaphos also foils the small hive beetle, Aethina tumida. Last
year, Florida beekeepers became the first in the United States to suffer major
losses from this shiny-black, quarter-inch-long insect.
Varroa mites not felled by fluvalinate or coumaphos might someday be
vanquished by natural compounds extracted from the smoke of burning citrus or
other plants. As entomologist Frank A. Eischen at Weslaco has already shown,
chemicals in some kinds of smoke can kill the miteswithout harming the
beesor at least make the mites fall off the bees. [See "Smoking Out
Research, August 1997, p. 19.]
Now, Elzen and her husband Gary, an insect toxicologist, have captured smoke
samples for analysis by Robert D. Stipanovic and colleagues in the ARS Cotton
Pathology Research Unit at Oxford, Mississippi. The scientists will use
instruments called mass spectrometers to identify the smoke chemicals. Ideally,
some of those extracts could be used in tomorrow's hives to quell the mites.
A family of varroa mites found at the bottom of a honey bee brood
Varroa mites have been implicated
in the spread of a pathogen known as Kashmir bee virus, but scientists don't
yet know the mites' exact role.
"It's possible that the mites, after feeding on the blood of a sick
bee, spread virus to the next healthy bee they attack," says entomologist
Akey C.F. Hung, who is at the ARS Bee Research Laboratory in Beltsville,
Maryland. "Or, if an otherwise healthy bee harbors a low level of the
virus, perhaps an attack by varroa mites triggers the virus to multiply."
To discover more about the microbe's spread, Hung is scrutinizing samples of
the virus' genetic material taken from sick and healthy bees and varroa mites.
"Although this virusin association with varroa mitescould
become a serious pathogen of bees," says Hung, "we don't yet know to
what extent it occurs in American beehives. If we can find out how Kashmir bee
virus is transmitted," he says, "we'll be better prepared to combat
it, should it prove to be a problem here."By
Marcia Wood and
Agricultural Research Service Information Staff, and Jill Lee,
formerly with ARS Information Staff.
This research is part of Animal Pests and Parasites, an ARS National
Program described on the World Wide Web at
For information about researchers named in this article, contact
Marcia Wood, USDA-ARS Information Staff, 800 Buchanan St., Albany, CA 94710;
phone (510) 559-6070, fax (510) 559-5882.
"Varroa-Tolerant Bees Keep Hives Buzzing" was published in
the August 1999 issue of
Agricultural Research magazine.