Glassy Winged Sharpshooter
You probably have heard this name in news reports or press releases at some point in time in the past year, and may be wondering exactly what it is and why it is receiving so much attention.
The Glassy-Winged Sharpshooter, whose scientific name is Homalodisca coagulata, has an appropriate name for a pest that causes death of plants by injecting a bacteria into the plant that plugs up the water-conducting tissues of the plant. This effect is known as “Pierce’s Disease”, and is particularly destructive to grape vines, one of the principle foods of the Sharpshooter.
While the media emphasis has stressed the damage to vineyards, there are many other plants that the Glassy-Winged Sharpshooter feeds on, and this compounds the problem. The University of California has identified at least 200 other trees and shrubs that serve as food for the sharpshooter, including citrus trees. While citrus trees, and perhaps others of the plants, are not harmed by the bacteria injected by the Glassy Winged Sharpshooter, their presence on these plants poses two major problems.
- Nurseries that grow and export affected plants are quarantined, and must spend a great deal of time and money to ensure their plants are not harboring the pest.
- Citrus groves potentially harbor the pest, and must be treated with pesticides that otherwise might not be needed for the production of the citrus. This may set back Integrated Pest Management programs that have been developed over the past 20 years.
Where did this pest come from?
The Glassy Winged Sharpshooter appears to have been introduced to California around 1990, coming from the southeastern United States, where it already was known as an agricultural pest. In California it was first noticed on eucalyptus trees, and then citrus trees, in southern California, but treated more as a novelty than a potential problem, as its future impact was not suspected at that time. It spread rapidly throughout all counties in southern California, and in the late ’90s began to show its damage to vineyards in some areas.
Where is it now?
In a California Farm Bureau news report in January 2000 it was stated that the GWSS was still restricted to the counties in southern California. Within a few months it was discovered in large numbers in Sacramento, 200 miles to the north, and by the end of the summer of 2000 was found another 100 miles north of that, including in the intense vineyard regions of Napa and Sonoma counties.
In August of 2000 the Oregon Dept. of Agriculture issued a quarantine on nursery materials that may be scheduled to be shipped into Oregon from Mexico, most of Southern California, and many southern states that are known to be infested with it. As of that time the GWSS had not been found in Oregon, and whether or not it can even survive there is not known, but around 10,000 acres of vineyards in Oregon would be at risk if it is imported and survives to pass Pierce’s Disease into the vines.
How does the GWSS cause the problems?
The Glassy Winged Sharpshooter is an insect in a group called the Auchenorrhyncha – a group that includes many common insects called cicadas, leafhoppers, planthoppers, and spittlebugs. All of them feed on plants by inserting their mouth – essentially a straw-like tube – into the plant, and sucking out plant juices. In the vast majority of cases the damage caused by these insects is not even noticeable, or is barely so. Sometimes their populations can be high enough that discoloration of the leaves or defoliation of the plant can occur. Other times sucking insects are responsible for passing on plant diseases, though, and this is the case with the GWSS.
Somewhere along the line the GWSS picked up a bacteria, called Xylella fastidiosa, that now is closely associated with the insect populations wherever they occur. It causes:
- Pierce’s Disease in grapes
- Phoney Peach Disease in the southern United States
- Variegated chlorosis of citrus in Brazil
- Oleander leaf scorch in southern California
Now, the Glassy Winged Sharpshooter doesn’t mean to infect plants with a disease, any more than a mosquito means to spread Malaria, but the association of the GWSS as a vector of plant disease does exist, and now must be dealt with in some way.
When the insect inserts its beak to feed on the plant it inadvertently inoculates the plant with the bacteria, which then multiplies rapidly inside the plant and produces a jelly-like material in the plant. This gel begins to plug up the tissues that conduct water through the plant, initially causing dieback of leaves and small stems. As the blockage increases the disease causes complete collapse and death of the entire plant. In grapevines this may be one to two years.
Other kinds of sharpshooters also are known to spread Pierce’s Disease to grapevines, but not nearly with the intensity that the GWSS can, due to its larger size, greater flight range, and rapid breeding activity.
What does the Glassy Winged Sharpshooter look like?
The GWSS has a typical appearance for the family of “leafhoppers” that it belongs to – long and cylindrical, with its wings held “roof-like” over the length of the abdomen. Its wings are relatively clear, giving it its common name, it has a brown to black color from above, a white underside to the abdomen, and many white or yellow spots on its head and upper thorax, which are unique to this species.
The GWSS also is a very large species, about ½” long, and is a strong flier, thus allowing it to spread over wide areas on its own. In warm areas, such as southern California or the southern U.S., the GWSS has two generations each year. The adults live about 2 months, with peaks of activity in winter and early summer. They lay their eggs on the leaves of the host plants, inserting the eggs just under the surface of the leaf tissue in groups of a few to as many as 27 eggs in a mass.
I don’t drink wine….what do I care?
As we’ve noted, the Glassy Winged Sharpshooter can cause death and destruction in many more plants than just grapevines, so its effect is felt by many crops and by backyard gardeners as well. Also, whenever a pest is able to hitchhike on plants there is a ripple effect felt across the country. Major nurseries are located in areas infested by the GWSS, and their plant materials cannot be sold and moved until extensive inspections, and possibly pesticide applications, are made to ensure the pests are not going with them. This also is occurring in California with the Red Imported Fire Ant, another recent import that has become well established in areas that grow nursery plants, and a pest that prefers to nest in the soil, often in the potted plants themselves.
Potentially, then, the presence of the GWSS can increase the cost of plant materials, increase the use of pesticides that otherwise would not be needed, and cause the death of a wide variety of agricultural and horticultural plants.
What is being done to control this pest?
It is felt very clearly by all who are involved – growers, applicators, regulators – that control of the GWSS cannot be done with widespread use of pesticides. These tools are used at this time in an effort to slow the spread of the insect while more effective long-term controls are developed. These take time.
Biological controls – almost all species of insects have their enemies. Often these are tiny wasps that generally are referred to as “parasitic” wasps, whereby the adult wasp lays her eggs in the pest insect, usually in the eggs or the early stages of nymphs or larvae. In the case of the GWSS a wasp parasite already had been identified and in use in Texas and Mexico, with some success, and this now is being bred in large numbers in insectaries at the University of California at Riverside. Initial releases of the wasp began in August in Riverside County in southern California, and more releases are planned for other heavy agricultural counties.
One concern that always is addressed when contemplating the use of living animals, such as these parasitic wasps, for the control of another living animal, is the fear that the parasite may become a bigger pest than the one it was intended to control. This is the reason for limited initial use and careful monitoring, to ensure the wasp doesn’t also have an effect on other desirable insects in our region.
Resistant plant varieties – a great deal of progress has been made in the past couple of decades, in developing varieties of plants that are resistant to diseases, and using these as much as possible. This is not necessarily “bio-engineering” or any other strange process. It simply can be selecting for those individual plants within a normal population that already are stronger or resistant, and using these as the parent stock to produce large quantities of offspring that also are resistant – a very natural process.
Obviously this is a very, very long term answer, and does not address the immediate need that growers have, to protect the crops they are already growing – crops that provide the income for the grower and his employees as well as the food for our tables. Rather than accept that your entire vineyard will be dead in a few years, and hope that alternatives can come around that allow you to make a living 10 years from now, the immediate protection offered by chemical pesticides may be necessary.
What can I do to help?
As with any of the many exotic, imported pests we become subjected to – Gypsy Moth, Japanese Beetle, Mediterranean Fruit Fly – the cooperation of the general public is vital. It is believed that Medfly may have been introduced into California in the 1980’s in coffee beans or fruit that was sneaked into the state in the suitcases of vacationers returning from Hawaii, who hated to admit to the Department of Agriculture inspectors that they had it.
Gypsy Moths hitchhike on the undercarriage of vehicles, as egg masses laid by the female, and those who come across the country from infested states, but don’t tell the truth to border inspection agents, risk spreading that devastating pest to other areas. The Red Imported Fire Ant now is thoroughly established in California, courtesy of bee hives that were infested.
Your cooperation with making quarantines effective will help keep pests out. By leaving plant materials behind, should they be growing in an infested area, or ensuring that they are “Certified” as clean, will help. It is believed that the GWSS made the 200 mile leap from southern California to Sacramento on nursery plant material. Should there be a need for Agriculture inspectors to inspect the plants on your property your friendly cooperation will help us all.