Glassy-winged sharpshooter
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| Homalodisca vitripennis (Germar), 1821 |
The Glassy-winged sharpshooter (Homalodisca vitripennis, formerly known as H. coagulata) is a large leafhopper insect from the family Cicadellidae, similar to other species of sharpshooter. It is about half an inch (12 mm) in length. Its color is dark brown to black with a black-and-yellow underside. It has 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. It is native to North America (northeastern Mexico), but has spread into the United States, where it has become an agricultural pest.
Glassy-winged sharpshooters usually lay a mass of eggs on the underside of leaves, and they cover the eggs with powdery white protective secretions kept in dry form (called "brochosomes") on the wings. After the glassy-winged sharpshooter 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 moltings or transformations, the nymphs become adult glassy-winged sharpshooters.
The glassy-winged sharpshooter feeds on a wide variety of plants. Scientists estimate that host plants for this sharpshooter include over 70 different plant species. Among the hosts are grapes, citrus, almond, 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. It feeds on a plant by inserting its needle-like mouth parts into the plant's xylem. While feeding, the glassy-winged sharpshooter excretes small droplets of a watery excrement, often called "leafhopper rain." This excrement is messy and, when dry, gives plants and fruit a whitewashed appearance.
Its feeding method, along with its voracious appetite for so many different hosts, makes the glassy-winged sharpshooter a vector for the Xylella fastidiosa bacterium. Once it feeds on an infected plant, the sharpshooter carries the bacterium to the next plant and transmits the disease while feeding. This spread can continue from plant to plant. A plant that is not affected by any of the diseases caused by Xylella fastidiosa becomes a reservoir, holding the bacterium for other sharpshooters to pick up and carry to other plants. Xylella fastidiosa is linked to many plant diseases, including phoney peach disease in the southern United States, oleander leaf scorch and Pierce's disease in California, and citrus X disease in Brazil.
Successful efforts using Integrated Pest Management, IPM, of the glassy-winged sharpshooter includes the use of insecticides, parasitoids (esp. 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 insects. 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 during high population densities and is spread among leafhoppers by contact with infected individuals, contact with virus contaminated surfaces, and/or as an aerosol in leafhopper excreta. The virus is specific to insects. 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.
[edit] References
- Grandgirard, J., M.S. Hoddle, G.K. Roderick, J.N. Petit, D. Percy, R. Putoa, C. Garnier, and N. Davies. 2006. Invasion of French Polynesia by the Glassy-Winged Sharpshooter, Homalodisca coagulata (Hemiptera: Cicadellidae): A New Threat to the South Pacific. Pacific Science, 60:4, 429-438.
- Hunnicutt, LE, Hunter, WB, Cave, RD, Powell, CA, Mozoruk, JJ. 2006. Genome sequence and molecular characterization of Homalodisca coagulata virus-1, a novel virus discovered in the glassy-winged sharpshooter (Hemiptera: Cicadellidae). Virology 350: 67-78.
- Hoddle M.S., Grandgirard J., Petit J., Roderick G.K., Davies N., 2006. Glassy-winged sharpshooter Ko'ed - First round - in French Polynesia. Biocontrol News and Information 27(3), 47N-62N
- Takiya, D.M., McKamey, S.H., Cavichioli, R.R. 2006. Validity of Homalodisca and of H. vitripennis as the Name for Glassy-Winged Sharpshooter (Hemiptera: Cicadellidae: Cicadellinae). Annals of the Entomological Society of America, 99: 648-655.
- Hunter, WB, Katsar, CS, Chaparro, JX. 2006. Molecular analysis of capsid protein of Homalodisca coagulata virus-1, a new leafhopper-infecting virus from the glassy-winged sharpshooter, Homalodisca coagulata. Journal of Insect Science 6:28, available online: insectscience.org/6.28/.
