Brookings, South Dakota
December 16, 2008
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SDSU
soybean research and Extension entomologist Kelley
Tilmon raises the parasitoid Binodoxys communis in an
SDSU greenhouse for release in South Dakota soybean
fields. The parasitoids are natural enemies of soybean
aphids |
A program supported by university
researchers, farmers and soybean groups is introducing tiny
parasitic insects to control soybean aphids in South Dakota and
neighboring states.
South Dakota State University
soybean research and Extension entomologist Kelley Tilmon said
there have been 10 releases of the insect, Binodoxys communis,
at points in eastern South Dakota since the program won federal
and state approval to proceed in 2007.
Tilmon is part of a group of 14
scientists from five north central states and the U.S.
Department of Agriculture who are overseeing the Binodoxys
communis release in South Dakota and the larger region.
“The thing to understand about these releases is that they’re
not mass releases of insects like butterflies at a wedding,”
Tilmon said. “Rather, these are small inoculations at various
points with the hope that over time, a population will become
established in that area and ultimately spread from there to
soybean fields throughout the state.”
In the long term, Tilmon said, the insects could make it
necessary to use pesticides less often to control soybean aphid,
an insect from Asia that was first discovered in the U.S. in
2000.
“Soybean aphid is actually seldom a pest in Asia, largely
because there is a large suite of natural enemies that are
particularly adapted to prey upon the soybean aphid,” Tilmon
said.
“This is a very common pattern: When an herbivorous insect —
something that’s going to be a crop pest — gets in accidentally,
it usually gets in without the natural enemies that help control
it in its land of origin, and as a consequence, usually becomes
a much larger pest in the new range than in its native range.”
One solution, Tilmon said, is to try to restore that balance by
what’s called “classical biological control.” In this case,
scientists performed research in the soybean aphid’s native
range, evaluated enemies of the pest insect and selected some
for further study.
University of Minnesota entomology professor George Heimpel said
scientists brought several parasitoids back to a
federally-approved quarantine lab at the University of
Minnesota, specially designed to prevent accidental release.
The parasitoids pose no threat to humans or pets, but scientists
wanted to evaluate whether they would harm other aphids besides
the soybean aphid.
At the Minnesota quarantine lab, researchers selected one that
preys almost exclusively on soybean aphid. Scientists filed an
application with the U.S. Department of Agriculture in January
2006 for permission to release the parasitoid.
Permission was granted in April 2007, after two experts from the
U.S., two from Canada and two from Mexico gave approval.
Tilmon said because Binodoxys communis is a soybean aphid
specialist, it’s not likely to cause problems for other non-pest
insects. In addition, the parasitoid doesn’t stray far from the
habitat of its host insect, making it unlikely to become a
nuisance for humans.
“These parasitoids are wasp relatives,” said Tilmon.
“They’re in the same family as wasps, but they’re not wasps in
the sense that we think of large, stinging creatures. These are
really more the size of gnats,” she described.
“I measured one once and it’s about the size of a comma at the
end of a sentence in your typical printed text. They are
biologically incapable of stinging people.”
As part of its reproduction cycle, Tilmon said the female
Binodoxys communis deposits an egg inside a living aphid. The
egg hatches into a larva that feeds inside the aphid. The aphid
eventually dies and forms a protective shell or “mummy” around
the developing parasitoid pupa. The adult parasitoid then exits,
leaving the mummified aphid shell behind.
Tilmon cautioned that only about half of the parasitoid
introduction attempts over the decades have resulted in
successful establishments. Even if the Binodoxys introduction is
successful, it won’t mean that producers need to stop monitoring
for soybean aphid and using pesticides to control aphid, but it
may mean they’ll need to spray less often. And if Binodoxys gets
established, whatever biological control it provides will be
free; producers won’t have to pay year after year for it.
The South Dakota Soybean Research & Promotion Council helps fund
Tilmon’s ongoing work.
"For soybean farmers, I think it will be very helpful to have
more options to control soybean aphids,” said Astoria producer
David Iverson, chairman of the South Dakota Soybean Research &
Promotion Council.
“Currently farmers can control aphids with pesticides,” he said.
“To have the aphid population reduced with natural predators
would be great for soybean producers and good for the
environment as well. We are fortunate to have Kelley Tilmon
doing this type of research.”
In addition, the North Central Soybean Research Program and the
Iowa Soybean Association use checkoff dollars to support the
biological control project against soybean aphid. The NCSRP was
recently nominated for the International IPM Achievement Award
for supporting this regional project, which has resulted in
releases in seven states.
In South Dakota, it’s a collaborate effort involving not only
SDSU research, but also the South Dakota Cooperative Extension
Service and South Dakota farmers. “Seven out of our 10 release
sites were done with the cooperation of Extension educators in
their respective counties, and they were done with the
cooperation of soybean producers on their farms,” Tilmon said.
“The soybean producers donated the space to set up the release
points and have helped to get this project going.”
“It’s really nice that this project has involved not just the
university, but also the grassroots of the soybean producers in
the state.”
As a result of her research and Extension work on several
fronts, Tilmon won the Sherwood and Elizabeth Berg Faculty Award
for 2007, given to an SDSU faculty member in the early stages of
a career.
Tilmon used the award to help fund her travel to attend the
International Congress of Entomology in Durban, South Africa, in
2008. The congress meets every four years in a different part of
the world. Tilmon presented work on the Binodoxys communis
project at the conference.
Heimpel notes that the University of Minnesota’s quarantine lab
and a USDA-sponsored quarantine lab in Delaware are studying two
other parasitoids for possible release against soybean aphid. |
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