• The glassy-winged sharpshooter, Homalodisca vitripennis (Germar), is a large leafhopper species native to the southeastern United States. It is one of the main vectors of the bacterium Xylella fastidiosa, a plant pathogen that causes a variety of plant diseases, including phony peach disease of peach and Pierce's disease of grape vector Pierce's disease.

  • These sharpshooters are about 12 millimetres (0.5 in) in length. Their color is dark brown to black with black-and-yellow undersides, with 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.

    They have piercing, sucking mouthparts and rows of fine spines on their hind legs.

    Glassy-winged sharpshooters usually lay a mass of eggs on the underside of leaves, and they cover them with powdery white protective secretions kept in dry form (called "brochosomes") on the wings. After the 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 molts, the nymphs become adult glassy-winged sharpshooters.

  • Damage

     

    Sharpshooter feeding does not cause damage in grape; however, these insects vector the bacterium Xylella fastidiosa, which causes Pierce's disease in grapes. (This bacterium also causes alfalfa dwarf disease and almond leaf scorch in California.) The blue-green sharpshooter is the most important vector of Xylella fastidiosa in coastal grape-growing areas. The glassy-winged sharpshooter is the primary vector in the Coachella Valley, Temecula, and Kern County. The green sharpshooter and the red-headed sharpshooter are present in coastal areas, but they serve as the primary vectors in most areas of the Central Valley.

  • When sharpshooters feed on vines, they inject the bacterium, which multiplies in the water-conducting system and causes water stress of the plant. Symptoms from early spring infections may become visible by fall of the year infected, but that is variety dependent. In vines infected the previous year, budbreak will be delayed or absent in spring, and leaf scorch appears by early summer and increases through fall, causing clusters to dry. Early-season infections (March-May) are more likely to survive the next winter than late summer infections and become chronic. Xylella fastidiosa can kill vines 1 to 3 years after infection.

    Distribution

     

    Though usually not a serious pest in the area of its native distribution, North America (northeastern Mexico), the glassy-winged sharpshooter has spread into the United States, where it has become an agricultural pest. It was introduced into Southern California, most likely through the nursery industry. The map of California shows the current distribution of the glassy-winged sharpshooter in southern California and the counties at risk of infection.

    The glassy-winged sharpshooter feeds on a wide variety of plants. Scientists estimate the host plants for this sharpshooter include over 70 different plant species. Among the hosts are grapes, citrus trees, almonds, 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. They feed on a plant by inserting their needle-like mouthparts into the plant's xylem. While feeding, sharpshooters squirt small droplets of waste from the anus (filtered xylem fluid, basically water with trace solutes, especially carbohydrates), often called "leafhopper rain." These droplets are messy and, when the water evaporates, leave a residue that gives plants and fruit a whitewashed appearance. Their feeding method, along with their voracious appetite for so many different hosts, makes glassy-winged sharpshooters an effective vector for the Xylella fastidiosa bacterium. Once they feed on an infected plant, X. fastidiosa colonizes the sharpshooter by forming a biofilm on its mouth-parts. The sharpshooter then transmits the disease to additional plants while feeding. A plant that is not affected by any of the diseases caused by X. fastidiosa becomes a reservoir, holding the bacterium for other sharpshooters to pick up and carry to other plants. X. fastidiosa is linked to many plant diseases, including phony peach disease in the southern United States, oleander leaf scorch and Pierce's disease in California, olive tree decline and citrus X disease in Brazil.

    Oleander leaf scorch

     

    Oleander leaf scorch is a disease of landscape oleanders (Nerium oleander) caused by a strain of X. fastidiosa which has become prevalent in California and Arizona, USA starting in the mid 1990s. This disease is transmitted by a type of leafhopper (insect) called the Glassy-winged sharpshooter (Homalodisca coagulata).

    Olive tree decline

  • The disease has been called olive quick decline syndrome (OQDS; in Italian: complesso del disseccamento rapido dell'olivo). The disease causes withering and desiccation of terminal shoots, distributed randomly at first but which then expands to the rest of the canopy. This results in the collapse and death of the trees.

  • Liquidambar styraciflua decline

     

    Leaf of Liquidambar showing distinct bands of discoloration between scorched and symptomless tissue caused by the bacterium, Xylella fastidiosa.

  • Management

     

    Successful efforts using integrated pest management (IPM) of the glassy-winged sharpshooter include the use of insecticides, parasitoids (especially wasps in the family Mymaridae), and the impact of naturally occurring pathogens like viruses, bacteria, and fungi. One of the newly discovered pathogens is a virus specific to sharpshooters. The leafhopper-infecting virus, Homalodisca coagulata virus-1 (HoCV-1,Dicistroviridae), has been shown to increase leafhopper mortality. The virus occurs in nature and is spread most readily at high population densities through contact among infected individuals, contact with virus-contaminated surfaces, and/or as an aerosol in leafhopper excreta. One of the most successful biocontrol efforts has been the mass rearing and release of four different leafhopper parasitoids (in the mymarid genus Gonatocerus), which have been very successful in reducing the number of eggs that survive. The traditional means of insect management, such as scouting and land owner reports of leafhopper presence, followed by highly focused insecticide treatments, have also been of great value in reducing leafhopper numbers; all of these impacts have produced a system wherein reasonable, environmentally sound management of this insect pest is being maintained.