The
information presented here is provided to answer common questions and concerns
of the general public. Should you require more information regarding glassy-winged
sharpshooters and Pierce's Disease, contact your local
county farm advisor or review some of the references
provided in this site.
The glassy-winged sharpshooter (GWSS), Homalodisca coagulata, is an insect native to the southeastern United States and is a new threat to California's crops and ornamental plants. This insect was first found in the southern part of the state in 1990, and it has been expanding its range northward ever since. GWSS vectors the pathogenic bacterium, Xylella fastidiosa, that causes Pierce's disease of grapes and leaf scorch of almonds and oleander, as well as diseases of many other crop and ornamental plants. GWSS often produce copious amounts of liquid excreta when they feed. This liquid, known as "sharpshooter rain", can be a nuisance in urban settings and can form chalky white deposits on citrus fruit resulting in a limited loss of commercial value. The glassy-winged sharpshooter is a member of the Order Homoptera in the group of insects known as the Auchenorrhyncha. Other insect representatives within the same order are cicadas, treehoppers, planthoppers, scales, spittlebugs and aphids. Sharpshooters are in the family Cicadellidae and are a kind of leafhopper. All Homopterans feed on plants by inserting sucking mouthparts into plants and are capable of causing direct plant damage if occurring in high numbers. Several species of Homoptera (like the glassy-winged sharpshooter) are important vectors of plant diseases.
Why should I care about the GWSS?
Glassy-winged sharpshooters transmit fatal bacterial diseases of several economically important agricultural crops. Specifically, this insect can transmit Pierce's disease of grapes, oleander leaf scorch, almond leaf scorch, alfalfa dwarf disease, citrus variegated chlorosis, phony peach disease, and probably a wide variety of scorch diseases of urban trees. Not all of these disease are known to exist in California; however, Pierce's disease of grapes, oleander leaf scorch and almond leaf scorch do occur in the state. Currently the sharpshooter is distributed throughout the southern part of the state, and its distribution is spreading. The glassy-winged sharpshooter has been implicated as the primary vector responsible for transmitting Pierce's disease through the Temecula winegrape growing area of Riverside County, California. The occurrence and spread of the glassy-winged sharpshooter within the state are now viewed as one of the most serious threats to California agriculture. Currently grape and almond production, and the associated products derived from those commodities, are at risk. There is additional risk to stone fruit and citrus production if the bacterial organisms responsible for phony peach disease and citrus variegated chlorosis are introduced to the state. When taken together, the glassy-winged sharpshooter and the diseases it vectors now threaten billions of dollars of the state's commodities. The potential economic fallout of losing just a single commodity (e.g. grapes) due to sharpshooter-vectored diseases would be disastrous. The economic fallout of losing several of these commodities is unheralded.
The glassy-winged sharpshooter was first detected in California near Irvine in 1989 and was later identified by the California Department of Food and Agriculture as a species common to the southeastern United States. It's previously described native range includes Florida, Georgia, North Carolina, South Carolina, Mississippi, Alabama, Texas, Missouri and Arkansas and northern Mexico. It is thought to have been established in southern California since about 1990, where it may have arrived as eggs on plant material.
What do glassy-winged sharpshooters look like?
The insect is one of the largest sharpshooters found in California and is almost twice as large as the other common species found in the state. Adults are about 1/2 inch (13-14 mm) long and dark brown in color with small yellow dots on head and thorax. Wings are membranous and translucent, with reddish veins. Egg masses are usually laid in the leaves of various plants but may also be deposited in the rind of citrus fruit, making it unmarketable. Upon trying to observe a sharpshooter on a plant, it will often retreat to the opposite side of the stem. Click here to go the workgroup webpage with links to photographs of the GWSS and other sharpshooters and leafhoppers of agricultural importance found in California.
How did this insect get the name "sharpshooter"?
One explanation for the term "sharpshooter" being applied to this insect comes from observing minute holes left by the female after laying eggs within cotton bolls. A second explanation for the term comes from copious amounts of liquid excreta that are ejected from the insect while it feeds. Because the sharpshooter feeds on the relatively nutrient-poor xylem tissues of its host plant, it must consume 100 to 1000 times its body weight in plant fluids to acquire the nutrients it needs. After filtering out the nutritious components of the xylem, the insect must excrete the excess fluid. This results in a constant "shower" of dilute liquid excreta that can be feel like a light rain when standing under heavily infested trees. Indeed many people call this "shower" a "sharpshooter rain"
How long does a GWSS live? Can it survive freezing weather?
Glassy-winged sharpshooter adults begin laying egg masses from February through May. The year's first generation matures as adults from May through August. In June through September, these adults lay the eggs that will become the year's second generation. It is this generation that overwinters in the adult stage and then produces the next year's offspring. The insect apparently is able to survive winter temperatures dipping as low as 20 degrees Fahrenheit. Whether our not it can withstand colder temperatures for any duration is unknown at this time.
Where can I find glassy-winged sharpshooters and what do they eat?
Currently in California, the glassy-winged sharpshooter is distributed throughout the southern part of the state (counties of San Diego, Riverside, Los Angeles, Orange, San Bernardino, Ventura, and portions of Santa Barbara and Kern).Click here to see the current distribution of GWSS in the state of California. The glassy-winged sharpshooter feeds on the xylem tissues of its host plants (The xylem is that portion of the plant that conducts water and nutrients up from the roots to the rest of the plant). The glassy-winged sharpshooter has an extremely wide host plant range including a wide variety of ornamental landscape plants, agricultural crops, and natural vegetation. Very high numbers of GWSS have been observed in citrus and avocado groves. A host plant list is maintained by the California Department of Food and Agriculture. Click here to see that list.
Can the GWSS invade areas where it does not currently exist?
Because GWSS can feed and lay eggs on such a wide variety of plants, it has the potential to increase its range in California. This species has been seen in high numbers in citrus along the coast of southern California since the early 1990s. During the past few years it has become locally abundant further inland in Riverside and San Diego counties. In 1998 and 1999 high populations on citrus and adjacent vineyards were seen in southern Kern County. The likelihood is very high that GWSS will spread ultimately northwards throughout the state. Currently, the "easiest" way GWSS are spread through the state is through transportation of commercial nursery products. As a result, state authorities have imposed agricultural quarantine restrictions on all nursery materials headed for areas of the state of California that currently do not have GWSS. State and county authorities are also closely monitoring areas of the state that do not currently have sharpshooters for the sudden appearance of these insects. In the event, new sharpshooter populations are found, eradication techniques are employed to prevent the further spread of this insect. Although quarantine restrictions and eradication efforts will certainly slow the spread of the insect, existing large populations of sharpshooters can disperse naturally. How fast sharpshooters are capable of dispersing naturally, under their own power, is currently unknown and is the focus of on-going research.
I think I found a glassy-winged sharpshooter. What should I do?
We need your help to determine the full extent of this insect's distribution in California. If you live in California, outside of the current range (click here to see the range) of the glassy-winged sharpshooter and you find insects matching the above description or suspect damage, please notify your local county agriculture commissioner or call the CDFA hotline at 1-800-491-1899. Insects may be placed in rubbing alcohol (70% isopropyl) in glass or plastic vials for identification. Please note where and when they were collected, and on which host plant they were found.
What can I use to kill glassy-winged sharpshooters on my plants?
Glassy-winged winged sharpshooters, all by themselves, are really not pestiferous. Currently, their occurrence in urban environments, under the worst of conditions, is only a mild nuisance (due to "sharpshooter rain"). Consequently treating for GWSS infestations by the homeowner is really not advised. As GWSS are capable of transmitting a number of fatal plant diseases (e.g. Pierce's disease of grapes, almond leaf scorch, and oleander leaf scorch), they are viewed as serious pests especially in agricultural situations. If you feel your plants are at risk of contracting one of these diseases as a result of sharpshooter feeding, please contact your local University of California County Extension Office or a local pest control advisor for control and management recommendations.
Are there any biological control agents available to kill the glassy-winged sharpshooter?
While
pesticides will continue to be the more common weapon against the glassy-winged
sharpshooter in large commercial vineyards, biological control agents, like
parasitic wasps, are an important tool in populated urban areas, organic vineyards
and wildlands, where pesticide applications are not feasible. Within the sharpshooter's
area of origin (S.E. United States, Northern Mexico) parasitic wasps, such as,
Gonatocerus triguttatus, successfully keep GWSS populations in check.
The wasp parasitizes the sharpshooter by laying its eggs inside those of the
sharpshooter. Once hatched, the wasps eat their way out of the sharpshooter
egg and leave a circular exit hole visible on the egg mass. University and CDFA
personnel are currently rearing and releasing parasitic wasps in organic citrus
groves and other locations throughout the state. Hopefully, these releases will
lead to permanent populations of these animals such that sharpshooter densities
are maintained at low levels. Researchers will continue to monitor how well
these wasps perform in the dry heat of California, how successfully they reproduce,
and how well they are able to find and destroy the eggs of the glassy-winged
sharpshooters.
Pierce's
disease is a fatal bacterial disease of grapes. It is caused by the organism,
Xylella fastidiosa. The bacterium blocks the xylem tissues of the plant.
Xylem tissues are the water- and nutrient-conducting vessels of plants. The
typical symptoms are for leaves on the plant to begin to dry or to scorch. Infected
vines can die in as little as one to two years. Pierce's disease has existed
for more than 100 years in the state, but until the arrival of the GWSS, there
really was not a "effective" vector capable of rapidly transmitting
the bacteria from vine to vine throughout a vineyard. Pierce's disease decimated
40,000 acres of grapes in the Anaheim, California area in the late 19th century.
It was dubbed "Anaheim disease", but the name was later changed in
honor of Newton Pierce, who studied the infection. The incurable plant disease
has appeared on and off ever since, but its spread and transmission has been
limited. Until the arrival of GWSS, the principal carrier, or vector, of Pierce's
disease in grapes, was the blue-green sharpshooter, a weak, small insect not
able to fly much further than three feet. Additionally the blue-green sharpshooter
does not prefer to readily feed on grapes, so that there is little vine-to-vine
transmission of the disease. Damage by Pierce's disease as a result of transmission
by the blue-green sharpshooter typically results in only the outer few rows
of a vineyard becoming infected. The GWSS has changed this scenario; it can
fly a long distance into a vineyard, and it readily feeds on grapes. The net
result is a insect vector that can quickly spread Pierce's disease throughout
an entire vineyard. Different varieties of Xylella fastidiosa also cause
almond leaf scorch, phony peach disease, alfalfa dwarf, oleander leaf scorch
and citrus variegated chlorosis. The glassy-winged sharpshooter is capable of
transmitting these diseases as well.
How does the glassy-winged sharpshooter spread Pierce's Disease?
Sharpshooters acquire the bacterium from infected plants and transmit it to healthy plants while feeding. The insect harbors the bacteria within its mouthparts. It only takes a few hours (sometimes only minutes) to acquire or transmit the disease. Thus, a healthy flying adult insect, that is moving around a vineyard, can theoretically transmit the disease to several plants a day. Juvenile stages of the sharpshooter loose the bacteria when they undergo a molt of the exoskeleton. They can readily re-acquire the bacteria by feeding on diseased plants. If the adult stage of the sharpshooter acquires the bacteria, the insect will harbor and be able to transmit the bacteria throughout its life (over 6 months). Once e a plant is infected with Pierce's disease, the plant can act as a reservoir of the bacterium. Any sharpshooter that feeds on the infected portions of the plant can pass on the infection to other plants.
How does the sharpshooter damage plants?
Direct feeding by the glassy-winged sharpshooter rarely damages plants. In certain instances, high densities of GWSS can cause economic damage to citrus fruit by depositing such large quantities of excreta ("sharpshooter rain") on the fruit such that its commercial value is reduced. GWSS are viewed as a very serious pest not because of their direct damage, but because they transmit fatal Xylella bacterial diseases (e.g. Pierce's disease of grapes, oleander leaf scorch, almond leaf scorch, etc). Currently it is not feasible to treat or cure these plant diseases. Consequently, once a susceptible plant acquires the disease, it will die.
What plants does the sharpshooter damage?
GWSS feed on a wide variety of plants with little noticeable damage. As mentioned above, GWSS are capable of transmitting Xylella bacterial diseases that are usually fatal to susceptible species of plants. Currently, plants at immediate risk to these diseases include commercial grapes (wine, table grape, raisons), almonds, oleander and to a lesser extent alfalfa. Certain strains of Xylella can also seriously affect citrus (citrus variegated chlorosis) and stone fruits (phony peach disease). At this time, the strains of Xylella causing these latter diseases are not known to occur in California.
The mouthparts of the glassy-winged sharpshooter are adapted to feed on plant fluids; they cannot bite humans. Glassy-winged sharpshooters do not vector any diseases that can harm humans. The bacterial diseases that the sharpshooter is capable of transmitting are only a threat to certain susceptible species of plants.
What does sharpshooter and Pierce's disease damage look like on plants?
You can see images on this website of sharpshooter damage to citrus fruit and damage to grapes, almonds and oleander due to the sharpshooter-vectored bacterial disease Xylella fastidiosa. Click here to go to the image section of this website.
Will my plants die if glassy-winged sharpshooters
are feeding on them?
With heavy infestations of GWSS, your plants may have a "whitewashed" appearance from the large amounts of liquid excreta deposited on the foliage. This white residue does not cause harm to plants and can be rinsed off with water. The long tem effects of heavy GWSS feeding on host plants are not well understood, but most plants appear to survive even heavy infestations of GWSS. If the glassy-winged sharpshooters are carrying the bacteria responsible for oleander leaf scorch and/or Pierce's disease of grapes, they can transmit these diseases to either oleander or grapes, respectively. If plants are infected with the bacteria they will in all likelihood die within a few years. There currently is no treatment or cure.
What is being done to control and manage the problem?
Currently, state-wide efforts to control and manage the sharpshooter-disease problem are being coordinated by the California Department of Food and Agriculture. Involved with these efforts are the local offices of the county agricultural commissioners, University of California Cooperative Extension advisors and specialists, and the United States Department of Agriculture Animal Plant Health Inspection Service. Management and control efforts vary depending on where you happen to be in the state. In areas of the state that currently do not have glassy-winged sharpshooters, efforts are directed at detecting and eradicating emerging populations. In agricultural areas of the state that have established populations of sharpshooters, efforts are directed at lowering overall population density such that the spread and incidence of disease will be minimized to the extent possible.
A number of federal, state, university and private scientists are currently studying the glassy-winged sharpshooter and the diseases it is capable of vectoring (see the workgroup directory on this website). The current research will result in an increase of our knowledge concerning the biology and control of Xylella bacterial diseases and their insect vectors. Much of this research is applied in focus with the direct aim of eliminating this serious agricultural problem. To see what research is currently being conducted, click here.
Where does money come from for necessary research?
Currently, funds for research come from a variety of sources. The following is a partial and every growing list of public and private agencies that are currently funding Xylella disease and sharpshooter research.
University
of California Glassy-winged Sharpshooter Workgroup Homepage
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email richard.redak@ucr.edu
