Distribution: Southern United States and northern Mexico except in very arid areas. Range recently extended into southern and central California and to Hawaii and French Polynesia.
Description: Adults about 1/2 inch (13-14 mm) long, dark brown color with small yellow dots on head and thorax. Wings membranous, translucent, with reddish veins.
Summary: The glassy-winged sharpshooter (GWSS), become established in California during the 1990s, probably introduced in the 1980s.. The glassy-winged sharpshooter (GWSS, Homalodisca vitripennis) has now become a major factor in Pierce’s disease and how California growers will deal with the problem. This vector of X. fastidiosa is a serious threat to California vineyards because of its more frequent and longer distance movements into and within vineyards compared to native sharpshooter vectors. In some cases, GWSS may also increase the rate of disease increase by moving the causal bacterium from vine to vine. It inhabits citrus and avocado groves and some woody ornamentals in unusually high numbers. At immediate risk are vineyards near citrus orchards.
From 1990 to 1994, GWSS was mistaken for a closely similar California species, the smoke tree sharpshooter (Homalodisca lacerta). What was unusual about GWSS was that it developed huge populations on citrus, crepe myrtle, avocado and several other species of woody ornamentals. GWSS was so abundant on citrus and some other plants that the residue from its excrement gives the trees on which it feeds a “whitewashed” appearance. This has alarmed citrus growers and homeowners, but so far the insect does not seem to be doing any direct damage to these plants, other than cosmetic damage to citrus fruits from egg masses deposited into fruits when populations of GWSS are high. This increases the danger of having a strain of X. fastidiosa bacteria that causes a serious citrus disease in Brazil arrive in California because the state now has an abundant vector on citrus. Because it feeds more often on oleander than other sharpshooters, GWSS is probably a major factor in the spread of oleander leaf scorch disease, which is caused by a newly introduced strain of X. fastidiosa.
GWSS has been seen in high numbers in citrus along the coast of southern California since the early 1990s. It also 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 And has occurred in Fresno County at least since the 1990s. Like many invasive species, GWSS may appear to have stabilized its distribution, then suddenly expand its range further.
GWSS probably first entered California as eggs on ornamental plants. The eggs are deposited into plant tissues. GWSS was first collected near Irvine in 1989 but not recognized as a newly introduced species until later. The leafhopper was identified (Calif. Dept. of Food and Agriculture) as a species common in the southeastern states from Florida through eastern Texas that occurs as far north as Missouri. GWSS is considered the prime vector of the bacterium X. fastidiosa to peach and grape in Georgia, Florida, and other southern states. These plant diseases are most common from central Florida to the immediate area near the Gulf of Mexico and the coastal plain of Georgia and South Carolina. Cold winter climates are hypothesized to limit the geographic distribution of the diseases (phony peach disease and Pierce’s disease of grapevine).
The main natural enemies of GWSS are several species of minute parasitic wasps that lay their eggs into the eggs of the sharpshooter. The relative abundance of GWSS in southern California appears to have steadily decreased since it began to be intensively studied in the early 2000s. [link to Hoddle video above]
The newly introduced GWSS is an effective vector of X. fastidiosa to peach and grape in Florida and Georgia. Although the transmission efficiency of GWSS (about 15 to 20% per insect per day) is less than that of other vectors such as the blue-green sharpshooter, its flight range and frequent movements make it a formidable vector for the spread of Pierce’s disease. Given its broad host plant range, GWSS could be a much bigger problem for California growers if different strains of X. fastidiosa that can cause disease in other crops become established within the state.
GWSS also feeds on dormant grapevines during the winter. Until more information about this aspect of glassy-winged sharpshooter’s role in spreading Pierce’s disease is available, growers should try to reduce numbers of glassy-winged sharpshooter present in vineyards at any time. Additionally, removing diseased vines as soon as possible when Pierce’s disease first appears in a vineyard may help reduce the infection rate. Early and vigilant disease detection and removal is recommended for any vineyards that experience influxes of the glassy-winged sharpshooter.
view a video on the threat of GWSS to California