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Fruit Perfume Lures
Female Codling Moths
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In the laboratory, entomologists
Alan Knight (left) and Doug
Light set up a flight tunnel
experiment to test which pear
odors attract female codling
moths.
(K9201-1)
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The luscious aroma of ripe pears
could spell doom to codling moths. Agricultural Research Service scientists
have discovered that a certain chemical in pears provides just the right
perfume to attract female codling moths to traps. That's a breakthrough that
may revolutionize integrated pest management (IPM) in apple, pear, and walnut
orchards worldwide—and will help growers to continue providing safe food
more economically.
Codling moths are the most severe and widely distributed pest of apples, pears,
and walnuts in the world. The moths were accidentally introduced into the
United States from Europe in the 1700s and have been a menace ever since.
Uncontrolled, the larvae—the worm in the apple—can destroy up to 95
percent of an apple crop and up to 60 percent of a pear crop. Feeding by larvae
creates holes in walnut hulls and shells that can allow fungi to enter and
infect the kernels. Some fungi produce toxins that at high levels are a food
safety concern. Both federal and international regulations prohibit growers
from selling toxin-contaminated nuts. |
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Codling moths of both sexes are
strongly attracted to a chemical
in pears.
(K9206-1)
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The Main Attraction
"Sex attractants called pheromones have been the main tool available to
growers for monitoring codling moths in orchards," says ARS entomologist
Douglas M. Light.
Pheromones, which are chemicals given off by female moths to attract males for
mating, have allowed scientists and growers to trap and monitor male moths in
orchards.
A synthetic version of the codling moth pheromone has been available for 30
years and provides the basis for mating-disruption programs. Growers can
disrupt the ability of males to find a mate by flooding the orchard canopy with
pheromone. Or they can time insecticide sprays according to the number of moths
found in traps baited with pheromone. |
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Entomologist Alan Knight
places a pear-based kairomone
trap in an apple orchard
to attract codling moths.
(K9204-1)
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Now Light has found a new,
potentially more useful tool.
"We've found a natural chemical in a fruit that is as effective as
pheromones in attracting moths. But more importantly, this compound not only
attracts males, it lures females," Light says. He works in the USDA-ARS
Plant Protection Research Unit at the Western Regional Research Center in
Albany, California.
While pheromone-based programs target male moths, the real goal has always been
to reduce the female's ability to reproduce. Females can lay 50 to 100 eggs,
and two or three generations can hatch each growing season. Attracting females
directly would allow growers to eliminate the females and their unlaid eggs and
to monitor mating cycles more precisely. |
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The high level of attractiveness of
the pear ester could be useful in
developing "attract and kill"
traps that reduce pesticide use while
removing moths from orchards before
they reproduce.
(K9205-1)
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"IPM programs are based on the
relationship between the time when male moths appear in pheromone traps and the
time eggs begin to hatch," says ARS entomologist Alan L. Knight. To
predict insect development, scientists use a measurement tool called a
degree-day model. For codling moths, eggs are believed to hatch after the
accumulation of 250 degree days—which ranges from 15 to 30 calendar
days—after the males emerge and are detected in sex-pheromone-baited
traps.
"There's a lot of potential error in estimating egg hatch based on the
number of males trapped," says Knight. "We think that being able to
monitor females should be a lot more accurate."
In field tests, Knight verified that the pear-derived attractant is more
effective than pheromones in monitoring—and potentially
predicting—mating and egg laying.
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Technician Kathy Reynolds, entomologist
Doug Light (center), and Trécé field
development manager Scott Lingren
inspect a trap baited with pear
ester for use in codling moth
monitoring in a walnut orchard.
(K9202-1)
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New Strategies Needed
"In the past, growers would use long-lasting insecticides that would cover
the range of possible days when moths could lay eggs and larvae could
hatch," Knight says. "But as environmental regulations require use of
less toxic and shorter-lived pesticides, it becomes important to know exactly
when the females mate and begin their egg laying."
Once the larvae hatch, there is only a short time before they crawl to and bore
into the developing fruit, where they are safe from external controls.
Although apples and pears generally suffer more from codling moth attacks,
Light was looking for a way to protect walnut orchards. He wondered if using
one of their preferred foods—pears—would lure the insects away from
the walnuts.
Finding What Rings Their Bell
Light worked with a team of ARS chemists at the Albany laboratory to obtain 37
combinations of the chemicals that make up pear odors and flavors. Improvements
in chemical detection methods over the last two decades allowed the scientists
to isolate and identify the many components that make up a wide range of fruit
and nut odors and flavors.
One of the mixtures showed extraordinary promise as a codling moth attractant.
They discovered that the key attractant was a chemical known as the pear ester,
or ethyl (2E, 4Z)-2,4-decadienoate.
To pursue the commercial potential of his discovery, Light established a
cooperative research and development agreement with Trécé, Inc.,
of Salinas, California. Clive Henrick, vice president of research and
development at Trécé, used synthetic chemistry techniques to
confirm that one key chemical in pears attracted the moths.
Pear ester, they found, acts as a kairomone. Unlike a pheromone, which involves
only one species, kairomones are chemicals emitted by one species—in this
case pears—that attract and benefit another, such as codling moths. The
moths have apparently evolved to detect this odor and use it to locate a
preferred food.
"There are a lot of known kairomones, but most are worthless for
commercial applications to monitor insects under field conditions,"
Henrick says. "This one is fantastic."
ARS and Trécé have applied for a patent on use of the pear ester
for codling moth monitoring and control.
Doing More With Less
Trécé also plans to include the attractant in a lure containing
insecticides. This attracticide will kill moths that contact it. "This
approach will use less than 10 percent of the amount of insecticide that would
normally be used," Henrick says.
Researchers estimate that 90 to 95 percent of male codling moths in an orchard
must be trapped or prevented from finding a mate to reduce the number of
fertile eggs laid to an economically manageable level. "But for each
female trapped, dozens of eggs are immediately eliminated," says Knight.
"Right now, there is no effective and economical way to determine how many
females are in an orchard," says Light. "Female lures may help
growers reduce pesticide use either by disrupting mating or by helping growers
time their pesticide use more precisely."—By
Kathryn Barry
Stelljes, Agricultural Research Service Information Staff.
This research is part of Food Safety (#108) and Crop Protection and
Quarantine (#304), two ARS National Programs described on the World Wide Web at
http://www.nps.ars.usda.gov.
Douglas M. Light is in the USDA-ARS
Plant Protection Research Unit,
Western Regional Research
Center, 800 Buchanan St., Albany, CA 94710; phone (510) 559-5831, fax (510)
559-5777.
Alan L. Knight is with the
USDA-ARS Yakima Agricultural Research
Laboratory, 5230 Konnowac Pass Rd., Wapato, WA 98951; phone (509) 454-6566,
fax (509) 454-5646. |
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"Fruit Perfume Lures Female Codling Moths"
was published in the June 2001 issue
of Agricultural Research magazine.
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