Author: Andria Cimino
Common Name: Glassy-winged Sharpshooter, Xylophagous Leafhopper
Scientific Name: Homalodisca coagulata (Say, 1832)
Classification:Phylum or Division: Arthropoda
Identification: Adults are large, almost half an inch (12mm) in length, dark brown or black, head and back stippled with ivory or yellowish spots. They have red-veined but otherwise transparent wings, from which their name is derived. Nymphs are wingless.
Original Distribution: Southeastern U.S. and northern Mexico (except for very arid areas)
Current Distribution: In addition to the above, found throughout Southern California as far east as San Bernardino County, and in patches as far north as Butte County.
Site and Date of Introduction: First sighted in CA in 1989, but mistaken for a native smoke tree sharpshooter until properly identified in 1994. Subsequent 1997 outbreak of Pierce's Disease in the Riverside vineyards of the Temecula region attributed to the glassywing sharpshooter, establishing it as a dangerous vector of the disease and an exotic pest requiring containment if not eradication.
Mode(s) of Introduction: Accidental introduction of glassy-wing sharpshooter egg masses on nursery stock transported from the southeast.
Reason(s) Why it has Become Established: The glassy-winged sharpshooter (GWSS) outcompetes the native sharpshooters (blue-green, smoke tree, and others). A voracious, generalist feeder, GWSS is known to subsist on over 70 species within 35 different plant families and is thought capable of further expanding its range of host plants and adapting to new habitats. It is active throughout the year, living in treetops where it consumes 10 times its weight in liquid an hour, feeding with a strawlike mouthpart it inserts into the xylem of its host plant.
At the first sign of cold weather, the GWSS "drops like a bomb" to overwinter in the leaf litter, where it can survive temperatures as low as 20º F. It produces high numbers with two generations born a year. It begins egg laying in late Feb. and continues through May. The first generation matures May through Aug. and begins the second egg laying from June through Sept. This generation will produce the next year's offspring. The GWSS can fly much further than any other sharp shooters, 3 to 16 feet compared to 3 feet for the smaller blue-green sharpshooter. There are native predators of sharpshooters, Gonatocerus ashmeadi and Pseneo kohlii, but they have little impact overall on the highly mobile, adaptable, and prolific GWSS.
Ecological Role: Herbivores play an important role in the food chain, providing food to pollinator species with their eggs and larva and breeding material as adults. The glassy-winged sharpshooter eggs are eaten by the Gonatocerus ashmeadi larva. The Pseneo kohlii uses the adult glassy-winged sharpshooters as a barrow for its larva. But mostly they function as pests in their new environment, a vector for diseases, especially the incurable Pierce's Disease, which rapidly kills their plant hosts.
Benefit(s): Perhaps there is some organism that benefits from the glassy-winged sharpshooter's excreta, which is copious and full of salts from the minerals and amino acids filtered out of the fluid consumed from plant xylem, but this has not been documented. Their removal from their new habitats would not leave a niche unfilled or upset the balance of the food chain.
Threat(s): As a vector of Pierce's Disease (PD), which decimates wine, table grape, and raisin crops, the glassy-winged sharpshooter poses a significant economic threat to the billion dollar viticulture industry of central CA. PD is an incurable disease, choking off a plant's ability to pump water and nutrients from the soil through its tissue (xylem) to its leaves. Diseased vines become nonproductive and usually die within 1-2 years. Although the bacteria that causes Pierce's Disease (Xylella fastidiosa) has been in CA for at least 100 years, the GWSS is a much more effective transmitter of the bacteria than the native sharpshooters. This is due to the GWSS's generalist feeding and breeding habits, greater mobility, and larger mouthparts. The latter enables it to feed on older wood and inject bacteria more deeply into the xylem.
Other sharpshooter species feed more on the edges of vines rather than the base stems, meaning infections are often cut away when the plant is pruned for the winter. But because of the GWSS feeding habits, infections are more often undetected until the next growing season, increasing the incidence of vine-to-vine transmission of the disease. Once it has picked up the bacteria, the GWSS carries it for life. With a much greater mobility than native sharpshooters (GWSSs can fly between 3 to 16 feet at a time, up to .25 miles a day), the GWSS has a much increased range as a vector.
Combined with its generalist feeding habits, there is concern that the GWSS will vector strains of X. fastidiosa that will induce disease in other valuable crops. The GWSS is a known vector of additional diseases, such as almond leaf scorch, phoney peach disease, alfalfa dwarf, oleander leaf scorch, and citrus variegated chlorosis. And because GWSS reproduces twice a year, it has substantially increased the population of insect vectors transmitting X. fastidiosa to vulnerable crops.
Control Level Diagnosis: High Priority. The exponential spread of Pierce's Disease since 1997 indicates the glassy-winged sharpshooter is a serious threat, having upset the tight control over spread of the disease by other native vectors and already caused $12-14 million of damage in grapevines in Temecula and threatens the billion dollar wine, raisin, and table grape region in central CA. Numerous additional crops are vulnerable as well. There is historical precedence that PD can wipe out entire agricultural industries, it decimated the CA grape industry in the 40s. Acres of cropland remain unplantable today due to presence of the bacteria.
Control Method: The California Dept. of Food and Agriculture (CDFA) worked in conjunction with the USDA, the County Agricultural Commissioners, the University of CA, and the agricultural industry to formulate the following guidelines for eradicating the Glassy-winged Sharpshooter:1. Inspect nursery stock moving from infested counties and from other states to slow the spread of the pestCDFA is also supporting greater research efforts to learn more about both the GWSS and Pierce's Disease. Most recently and successfully, the University of CA Riverside discovered a predatory wasp, Gonatocerus triguttatus, that is a natural enemy of the GWSS in Mexico and Texas. It parasitizes GWSS eggs, laying its eggs inside of them. When the wasps hatch, they eat their way out. This new exotic is being released in limited numbers in Riverside Co. to combat the GWSS. Additional releases are planned. Although pesticides continue to be the more common weapon against the GWSS, the exotic wasp shows promise for urban areas, organic vineyards, and wildlands, where pesticide use is not feasible.
2. Conduct a statewide survey to determine the distribution of the GWSS
3. Establish multicounty pest management areas to begin treatment in infested areas or to develop contingency plans to prepare for infestation
4. Conduct an aggressive public outreach to educate growers and others about the seriousness of the problem.
Other scientists are investigating how to prevent PD, such as by boosting grapevines' levels of essential plant micronutrients or finding the genetic sources of resistance to PD in muscadine grape varieties. However, grape breeding is a slow process and it is estimated that, once found, it will take at least 10 years to successfully transfer this gene or genes of resistance into wine-producing varieties.