Though small and gentle, the glassy-winged sharpshooter can pose a
major threat to familiar plants such as orange, lemon, and almond trees;
grapevines; and oleander bushes; as well as to alfalfa and coffee.
In fact, this invasive insect represents a multibillion-dollar hazard
to American agriculture. That's mainly because of its impressive ability
to spread a plant-disease-causing bacterium, Xylella fastidiosa.
Both insect and microbe are harmless to humans.
Scientists don't yet know how to sufficiently control Xylella.
The same is true for the little leafhopper.
The leafhopper has some peculiarities that make it especially difficult
to combat. Apparently, it can thrive exclusively on the sap that it
sucks from target plants. It is remarkably effective at extracting whatever
nutrients the sap might contain.
Efforts of ARS scientists and their co-investigators to rein in Xylella
and the sharpshooters have won them a USDA Honor Award (see page 17).
Besides developing short-term solutions, such as insecticides and repellents,
ARS is investigating tactics
that may give long-term control.
- We are exploring many details about how the sharpshooters transmit
Xylella; where the insect chooses to rest, feed, and lay its
eggs; how some plants resist Xylella; and how to tell one strain
of Xylella from another (see story, page 16).
- We are identifying the range of plant species that certain Xylella
strains can infect.
- We are testing several species of tiny, stingless wasps, the sharpshooters'
natural enemies, to see whether they can quash expanding sharpshooter
populations (see story, page 18).
- We are experimenting with long-term cold storage of sharpshooter
eggs that provide a home and food for the eggs of these wasps. When
wasp young hatch, they feed on sharpshooter eggs, killing sharpshooter
young. Successful storage of wasp-occupied sharpshooter eggs could
give us a reliable supply of wasps to deploy at sharpshooter-infested
- We are investigating another natural enemya fungus that is
harmless to plants but may be a potent foe of sharpshooters.
- We have cooked up new meals that can be fed to laboratory-reared
sharpshooters. We need large indoor populations of them for our tests
of biological control agents, such as the fungus and the wasps, or
for tests of environmentally safe insecticides.
- We are zeroing in on sharpshooter genes, with the intent of disrupting
those critical to the insects' ability to develop strong wings and
to produce viable eggs.
- We recently funded an ambitious and successful venture to decipher
all the genetic material in the X. fastidiosa strain that afflicts
grapes, causing what's known as Pierce's disease. This analysis of
the X. fastidiosa genome will provide clues to vulnerabilities
that we might be able to exploit. The American Vineyard Foundation,
the California State Department of Food and Agriculture, and Brazil's
São Paulo State Research Foundation were our partners in sponsoring
In planning our sharpshooter research and our other investigations
of unwanted invasive or exotic organisms, we coordinate with the National
Invasive Species Council. The council is composed of pros from USDA
and other federal departments and agencies.
Interestingly, even though the glassy-winged sharpshooter is native
to Texas and the southeastern United States, it meets the council's
definition of an invader: "Any plant, animal, or organism that
is not native to the ecosystem under consideration and whose introduction
is likely to cause harm to human health, the environment, or the economy."
The sharpshooter squarely fits this profile. It has wandered from its
native range, first showing up in southern California in 1989. It has
wreaked agricultural havoc there, spreading X. fastidiosa that
killed 50 to 90 percent of the grapevines in affected vineyards within
only 2 to 3 years.
The variety of crops that the glassy-winged sharpshooter attacks and
the assortment of costly X. fastidiosa strains that it transmits
warrant our nationwide efforts to rein in this invasive pest. We have
carefully apportioned key aspects of the insect-bacterium-plant interactions
into researchable projects. And we have expanded our staffing to broaden
the array of scientific specialties that we are bringing to bear on
this problem. Our approach may serve as a model for other federal "first-responder"
research strategies to counteract the menace of invasive or exotic organisms.
Kevin J. Hackett
ARS National Program Leader
"Forum" was published in the September
2003 issue of Agricultural Research magazine.