This Colorado potato beetle is being offered a choice between a chemical
attractant and potato leaf aromas and is moving toward the
attractant. (K8743-1)
Ever wonder how insects find exactly
what plant they want to eat? Entomologist Joseph C. Dickens has found the
answer to that question—at least for one key potato pest. Because of his
inquisitiveness about Colorado potato beetles, there's good news for growers:
An attractant may not be far away.
For at least 73 years, scientists have been searching for a scent that attracts
this yellow and black bug to solanaceous plants. Colorado potato beetles are
the potato crop's most destructive insect pest, costing growers millions in
chemical control and crop losses each year.
By placing tiny electrodes on the tips of their antennae and monitoring their
sensitivity, Dickens, who is with ARS'
Vegetable Laboratory in Beltsville, Maryland, discovered several chemical
scents that attract the pests. He exposed the insects to different potato leaf
aromas and allowed them to choose those they preferred.
A gas chromatograph (GC) is
used to identify individual scents
emitted from potato foliage.
Above, entomologist Joseph
Dickens positions a Colorado
potato beetle antenna in front
of a GC outlet to find out which
scents the insect detects. (K8742-1)
When Dickens offered the beetles a
choice between one of the attractive scents and potato foliage, the beetles
were terribly confused, he says, and they eventually responded randomly.
"We separated odors from both normal and wounded plants using a gas
chromatograph, which separates chemical mixtures into components," says
Dickens. "This allowed us to stimulate the beetles' antennae with the
individual components to see which they could smell. We monitored the insects'
responses to both real and synthetic scents. So far, we've tested 16 different
synthetic chemical blends, and we hope to develop and test more."
During summer 1998, Dickens was surprised to find in a preliminary field test
that the beetles were captured with a synthetic lure containing a mixture of a
few of these compounds. He says no one had ever caught a Colorado potato beetle
with a synthetic lure before. He and his colleagues have identified at least
five different synthetic blends that are attractive to the insects in
laboratory tests and may work in the field as well.
"From this research, naturally occurring chemical signals could be used to
monitor and control pest populations," Dickens says.
He is also investigating how chemical scents, which are emitted when the
beetles chew on plants, might help attract potato beetle predators. Two
predators of interest are spined soldier bugs and two-spotted stink bugs.
Dickens has already identified chemical blends that are attractive to both.
Down the road, these chemical blends could be used as part of a biological
control effort using natural enemies to control Colorado potato beetles, thus
reducing reliance on pesticides.
Growers frequently apply insecticides to control the critter, but it has armed
itself with resistance to many chemicals. "Our ultimate goal," says
Dickens, "is to develop a synthetic attractant to combine with a toxin or
pathogen in a bait, which could be used to control this pest." —By
Tara Weaver-Missick,
Agricultural Research Service Information Staff.
This research is part of Crop and Commodity Pest Biology, Control, and
Quarantine (#304), an ARS National Program described on the World Wide Web at
http://www.nps.ars.usda.gov/programs/cppvs.htm.
Joseph C. Dickens is at the
USDA-ARS Vegetable
Laboratory, Bldg. 010A, Room 112, 10300 Baltimore Ave., Beltsville, MD
20705-5374; phone (301) 504-8957, fax (301) 504-5555.
"The Nose Knows" was published in the
February 2000 issue of
Agricultural Research magazine.
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