October 14, 2004, ARS News Service: A natural fungus could
be a nonchemical alternative for beekeepers looking
for ways to control the parasitic varroa mite, according
to Agricultural Research Service scientists in Weslaco,
For several years, scientists in the ARS Beneficial
Insects Research Unit at Weslaco have been looking for
a natural organism that's harmless to bees but kills
New, nonchemical controls are needed because the mite
has developed resistance to the only approved chemicals--fluvalinate
and coumaphos--now used against varroa. So the researchers
looked at various organisms, tried different dosages
and application methods, and conducted toxicity tests.
Finally, they selected strains of the fungus Metarhizium
anisopliae that proved highly pathogenic to the mites.
This potent fungus, which also kills termites, doesn't
harm bees or affect queen reproduction. To test the
fungus, 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 the strips, thereby spreading the
spores to the whole colony.
In field trials, once the strips treated with M. anisopliae
were inside the hives, several bees quickly made contact
with the spores. Within 5 to10 minutes, all the bees
in the hive were exposed to the fungus, and most of
the mites on the bees died within three to five days.
The fungus provided excellent control of varroa without
impeding colony development or population size. Tests
showed that Metarhizium was as effective as fluvalinate,
even 42 days after application.
The scientific team is now fine-tuning the strategy
for transfer to producers.
Read more about this research in the October 2004 issue
of Agricultural Research magazine, available online