Scientists Sharpen Strategies To Sabotage Glassy-Winged
Glassy-winged sharpshooter on
a grape leaf.
|A half-inch-long insect called the
glassy-winged sharpshooter has wreaked havoc in southern California wine
vineyards, causing an estimated $14 million in damage during the past several
years. The sharpshooter carries the Xylella fastidiosa bacterium, the
cause of the incurable Pierce's disease of grapevines. Known to scientists as
Homalodisca coagulata, the lively leafhopper is now set to attack other
grape-growing regions in the Golden State as well.
To rout this pest, scientists at ARS
labs from coast to coastand in South Americaare making the
sharpshooter and the Xylella microbe the focus of ambitious new studies.
The researchers are investigating promising particle films, insecticides, and
biological control agents that might sabotage the sharpshooter. They're delving
into the basic biology of both the insect and the bacterium. And they're
pursuing new ways to quickly and easily detect the microbe in sharpshooters and
in afflicted plants.
Here's a look at some of those investigations.
Grape vines are a
favorite target of
|A Particle Spray Keeps
A coating of white kaolin particles, co-developed by ARS entomologist Gary J.
Puterka, can make grapevines inhospitable to sharpshooters.
"The specially shaped and sized particles stick to the sharpshooters' legs
and wings when they land on treated foliage, making it a very uninviting place
for dining on or laying eggs," explains Puterka. He is with the ARS
Appalachian Fruit Research Station in Kearneysville, West Virginia.
The product, sold by Engelhard Corporation under the trade name Surround WP
Crop Protectant, has been very successful in protecting pears and apples from
"Given a choice between treated and untreated foliage, glassy-winged
sharpshooters are highly unlikely to settle on Surround-treated foliage,"
says Puterka, who tested it this year on table grapes growing in central
California's Kern County. The vineyards he used border citrus groves, which can
harbor the sharpshooter.
At the University of
California at Riverside,
ARS technician Doug Diaz
(left) and field worker
Vince Lyons count glassy-
winged sharpshooters on a
grapevine treated with
| Puterka and collaborators wanted to
see if Surround would prevent the six-legged varmints from moving into the
vineyards after wintering in citrus. After three treatments from mid-March
through mid-April 2001, the scientists found that the number of sharpshooter
trap catches and eggs was far lower in the Surround-treated areas than in the
Puterka got similar results from a larger pilot study in Kern County. It is the
first project aimed at developing an economically feasible, areawide strategy
to quell the pest. Specialists from California state and county agencies, along
with 30 growers and numerous advisors, are part of the study, which is
coordinated by USDA's Animal and Plant Health Inspection Service (APHIS).
"Participating growers use products that have minimal toxicity, whenever
possible, in order to spare beneficial insects," says APHIS entomologist
Matthew A. Ciomperlik. "Surround, which is completely nontoxic, clearly
outperformed insecticides and is proving to be very economical and effective at
preventing the insect's spread. Growers needed to use only three applications
of Surround versus six of insecticides. So Surround might help them cut costs.
Some growers who were reluctant to try Surround changed their minds when they
saw how effective it was."
Donald A. Luvisi, a Kern County farm advisor with the University of
California's Cooperative Extension Service, sees Surround as very promising for
early-season use. But after the vines bloom, he notes, table grape growers
would have to switch to insecticides. "The Surround treatment, if
continued, would leave a white residue on the stems," Luvisi explains.
"The residue is harmless, but it probably would be unacceptable to
Matthew Blua, entomologist
at University of California
at Riverside, beats an
orange tree to shake
To learn more about insecticides that can safely and effectively zap the
sharpshooter, ARS researchers David H. Akey and Thomas J. Henneberry of the
Western Cotton Research Laboratory in Phoenix, Arizona, have teamed up with
entomology professor Nick C. Toscano of the University of California at
Riverside to scrutinize some of the most promising compounds.
In one series of experiments, they took sharpshooters that were living on
citrus trees and moved them to a southern California vineyard of Chardonnay
grapes. On one vine in each plot, the scientists enclosed 25 sharpshooters in
an improvised cage made of soft netting. They then sprayed an insecticide in
two applications, spaced 1 week apart. They repeated this procedure in their
tests of about two dozen different insecticides.
The researchers inventoried the cages for dead sharpshooters at 6 hours and at
1, 2, and 6 days after spraying. Then, for the next 15 to 29 days, they
periodically restocked the cages with new sharpshooters to determine whether
the aging residue of the chemicals had any effect on the insects.
"We were particularly concerned with how fast the insecticides knocked
down the sharpshooter," says Henneberry. "That's especially important
if an insecticide is used for stopgap protection when a new infestation is
discovered. Not all scientists agree about exactly how fast a feeding
sharpshooter can transmit the bacterium into a grapevine. But, in the ideal
scenario, the insecticide would kill the sharpshooter before the bacterium
could enter the plant."
This parasitic wasp, Gonatocerus
triguttatus, lays its eggs
in glassy-winged sharpshooter
eggs embedded in a leaf.
| In general, compounds
known as pyrethroids and neonicotinoids were the best performers, according to
the researchers. One pyrethroid killed all the caged sharpshooters within 6
hours. Based in part on the team's studies, the pyrethroid cyfluthrin is
already approved for sharpshooter control. Pyrethroid and neonicotinoid
residues were still killing sharpshooters after 28 days.
Seeking Egg Parasitoids
One of the trickiest aspects of using these or other insecticides is making
sure that the chemicals don't clobber beneficial insects, such as natural
enemies of the sharpshooter. Among the sharpshooter's most formidable foes, for
example, are egg parasitoidsinsects that unabashedly lay their eggs
inside sharpshooter eggs. Parasitoid young hatch inside the sharpshooter eggs,
then proceed to feast on them.
One egg parasitoid, a tiny, stingless wasp called Gonatocerus
triguttatus, has already been released in California by researchers at the
University of California at Riverside and APHIS. Now, ARS-sponsored studies may
uncover other promising parasitoids.
At the ARS South American Biological Control Laboratory in Hurlingham,
Argentina, researchers are investigating the parasitoids that emerge from the
eggs of a native South American sharpshooter, Tapajosa rubrimarginata.
"In field experiments so far, we've found that parasitoids emerged from 66
to 71 percent of the eggs. That's a fairly impressive rate of parasitization
for an experimental situation," says Guillermo Logarzo. He is based at the
Serguei V. Triapitsyn, a wasp expert from the University of California at
Riverside, is collaborating with the Hurlingham scientists. Some of the
Argentine species of wasps that he has identified so far are very different
from parasitoids that beleaguer the sharpshooter in North America.
The ARS Beneficial Insects Research Unit in Weslaco, Texas, is helping fund the
Hurlingham studies. Says Walker A. Jones, who leads the Weslaco research unit,
"Parasitoids or other sharpshooter natural enemies from subclimates
similar to the grape-growing regions of California might outperform natural
enemies imported from other climates. Our survey of areas where sharpshooter
species occur showed that subclimates in some areas of Argentina match those of
California. In addition, Chile has some exact matches, so it's being included
in explorations for new biological control agents."
But researchers aren't ruling out potential biological control agents from
other regions. For instance, the Weslaco scientists and their colleagues are
hot on the trail of an egg parasite found in south Texas and in northeastern
Mexico. Notes Jones, "We think this parasitoid is at least partly
responsible for the lack of glassy-winged sharpshooters in that region."
Wood, and Judy McBride,
Agricultural Research Service Information Staff.
This research is part of Crop Protection and Quarantine, an ARS National
Program (#304) described on the World Wide Web at
Gary J. Puterka is with the
USDA-ARS Appalachian Fruit Research
Station, 45 Wiltshire Rd., Kearneysville, WV 25430; phone (304) 725-3451,
ext. 361, fax (304) 728-2340.
David H. Akey and
Thomas J. Henneberry are
with the USDA-ARS Western Cotton
Research Laboratory, 4135 E. Broadway Rd., Phoenix, AZ 85040; phone (602)
437-0121, fax (602) 437-1274.
Guillermo Logarzo is with the
USDA-ARS South American Biological Control Laboratory, Bolivar 1559, 1686
Hurlingham, Argentina, phone/fax 53-11-4662-0999.
Walker A. Jones is in the
USDA-ARS Beneficial Insects Research Unit,
Kika de la Garza Subtropical
Agricultural Research Center, 2413 E. Highway 83, Weslaco, TX 78596; phone
(956) 969-4852, fax (956) 969-4888.
"Scientists Sharpen Strategies To Sabotage
Glassy-Winged Sharpshooter" was published in the
issue of Agricultural Research magazine.