Glassy-winged

Sharpshooter and

Pierce’s Disease in

California

The glassy-winged sharpshooter is a devastating

new pest for California. While the pest is not a problem in the Southeast United States, since its migration into California in 1990, the glassy-winged sharpshooter population there has ballooned. It can now

be found throughout southern California.

This pest is a concern to California agriculture

because of its ability to transmit Xylella fastidiosa, a

bacterium that causes a variety of plant diseases

including Pierce’s disease, which threatens

California’s wine and table grape industry. The

glassy-winged sharpshooter flies further than native

sharpshooters, making the possibility of the bacterium’s increased spread a serious agricultural threat.

Glassy-winged Sharpshooter

The glassy-winged sharpshooter is about 0.50 of

an inch (12mm) in length. Its color is dark brown to

black with a black-and-yellow underside. It has yellow eyes, and the upper parts of the head and back

are speckled with ivory or yellowish spots. The wings

are transparent with reddish veins.

The glassy-winged sharpshooter feeds on a wide

variety of plants. Scientists estimate that host plants

for this sharpshooter include over 70 different plant

species. Among the hosts are grapes, citrus,

almond, stone fruit, and oleanders. Because of the

large number of hosts, glassy-winged sharpshooter

populations are able to flourish in both agricultural

and urban areas.

Glassy-winged sharpshooters usually lay a mass

of eggs on the underside of leaves. After the glassywinged sharpshooter nymphs hatch, the remaining

egg mass leaves a brown mark on the leaf’s surface.

The nymphs feed within the vascular system of the

small stems on the plant where the eggs were

deposited. After several moltings or transformations,

the nymphs become adult glassy-winged sharpshooters.

The sharpshooter feeds on a plant by inserting

its needle-like mouth parts into the plant’s xylem (the

water-conducting tissues in the plant). While feeding,

the glassy-winged sharpshooter excretes small

droplets of a watery excrement, often called “leafhopper rain.” This excrement is messy and, when dry,

gives plants and fruit a whitewashed appearance.

Its feeding method, along with its voracious

appetite for so many different hosts, makes the

glassy-winged sharpshooter a vector for the Xylella

fastidiosa bacterium. Once it feeds on an infected

plant, the sharpshooter carries the bacterium to the

next plant and transmits the disease while feeding.

This spread can continue from plant to plant. A plant

that is not affected by any of the diseases caused by

Xylella fastidiosa becomes a reservoir, holding the

bacterium for other sharpshooters to pick up and

carry to other plants.

Pierce’s Disease 

The bacterium Xylella fastidiosa is linked to many

plant diseases, including phoney peach disease in

the southern United States, oleander leaf scorch and

Pierce’s disease in California, and citrus X disease in

Brazil.

Pierce’s disease has long been a scourge to

California’s vintners. In the 1880s, the disease infected over 40,000 acres of grapes around Anaheim,

devastating vineyards.

Over the years, California producers learned to

cope with the disease. With the introduction of the

glassy-winged sharpshooter, however, the spread of

Pierce’s disease has increased dramatically. In 1998,

the Temecula area of Riverside County, CA, had a

few localized areas of Pierce’s disease. A recent

report indicates now that about 30 percent of

Temecula vineyards are infected with Pierce’s 

disease.

When a vine becomes infected, the bacterium

causes a gel to form in the xylem tissue of the vine,

preventing water from being drawn through the vine.

Leaves on vines with Pierce’s disease will turn yellow

and brown and eventually drop off the vine. Shoots

will also die. After 1 to 5 years, the vine itself will die.

With the spread of the glassy-winged sharpshooter, the spread of Pierce’s disease has become

a threat to California’s entire wine and table grape

industry. The proximity of vineyards to citrus

orchards compounds the threat because citrus is not

only a host for the sharpshooter eggs, but it is also a

popular overwintering site for the insect.

Controlling the Disease

No one action can stop the spread of this disease. Instead, a multi-pronged approach must be

used to control both the glassy-winged sharpshooter

and Pierce’s disease. The U.S. Department of

Factsheet

Plant Protection and Quarantine December 2002

APHIS
Agriculture (USDA) has already allocated more than

$20 million toward control of the glassy-winged sharpshooter.

In addition to supplying funding for critical

research and control, USDA’s Animal and Plant

Health Inspection Service (APHIS) is working with the

California Department of Food and Agriculture (CDFA)

to survey for this insect pest in order to find out exactly where it has become established and where it is

headed.

USDA and University of California (UC) scientists

are also looking at biocontrol methods to counteract

the sharpshooter. Biocontrol methods rely on a pest’s

natural enemies to control its spread.

In August 2000, CDFA and UC scientists released

hundreds of tiny parasitic wasps imported from northern Mexico in Riverside and Temecula, CA. The parasitic wasp lays its eggs inside sharpshooter eggs,

killing them. The results of this test release will be

studied to determine whether the natural enemies are

an effective control method.

At the same time, USDA researchers are conducting DNA analysis that could be critical in determining

what biocontrol agents will work best against this

pest. The researchers want to find out whether the

glassy-winged sharpshooter that now inhabits the

southwestern United States has the same genetic

make-up as the glassy-winged sharpshooter that is

native to areas of similar climate in Mexico.

Researchers are also looking for the pest in Central

America as well as any natural enemies in that region.

The results of this research should help shed light on

whether the parasitic wasp native to Mexico as well as

natural enemies from other parts of the world are an

appropriate method of control. If these natural enemies fail to effectively control the glassy-winged

sharpshooter, APHIS’ scientists will search the world

for an alternative that can control the pest without

negatively impacting the environment or other

species.

In addition to biocontrol, USDA is conducting

research on environmentally friendly chemicals, or

biorationals, that could be used in combination with

other control methods in the fight against the glassywinged sharpshooter. Researchers are looking for

biorationals that will kill sharpshooter eggs but not

beneficial insects.

Finally, Pierce’s disease must be addressed as

well. Researchers recognize that to ignore Pierce’s

disease and only concentrate on the sharpshooter will

not solve California’s problem. Scientists have

already initiated this research, but it is still too early to

know the results of their work in this area.

It is USDA’s goal to provide California with the

research and tools to fight both the glassy-winged

sharpshooter and Pierce’s disease. In cooperation

with CDFA and the University of California, USDA is

working to provide relief to California’s grape growers

and safeguard American agriculture from plant pests

and diseases.

United States Department of Agriculture • Animal and Plant Health Inspection Service • Safeguarding American Agriculture

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