San FranciscoState University
Department of Geography

Geography 316:  Biogeography

The Biogeography of
  Glassy-winged sharpshooter (Homalodisca coagulata)
  by Greti Wolf, student in Geography 316, Fall 2000

 
Homalodisca coagulata, The Glassy-winged Sharpshooter.
 
Kingdom: Animalia
Phylum:Arthropoda
Class:Insecta
Order:Hemiptera
Family:Cicdellidae
Genus:Homalodisca
Species:  Homalodisca coagulata
 
Description of Species:
Homalodisca coagulata, theGlassy-winged Sharpshooter, is a large (13-24 mm long) dark brown insect. Adultshave small yellow spot marking the head and thorax. The wings are translucent,with red veins, and give the animal its “glassy” appearance. The underside of the abdomen is white.

Homalodisca coagulata are xylem feeders, using their long sharp mouth parts to pierce the surface o ftheir host plants. The xylem is the conductive tissue of the plant, which transports fluids and salts from the roots upwards through the plant (Jones, etal 1992). Homalodisca coagulata is an effective vector of bacterial plant pathogen (Phillips 1999). Homalodisca coagulata belongs to the Family Cicadellidae: the leafhoppers. Leafhoppers are serious pests in cultivated crops, especially citrus orchards and vineyards. Some species of leafhoppers excrete a clear watery fluid from the anus known as "honeydew". This substance attracts other insects that cause further damage to the plant.(Borror  1970).
 
Distribution:
Originally from the southeastern United States and northern Mexico, Homalodisca coagulata, the Glassy-winged Sharpshooter, has recently spread to California. The insect was first discovered in California in 1990 (in Ventura County). Previous specimens had been collected in 1989, but were not recognized as a seperate species until later. Within two years Glassy-winged Sharpshooters had spread to San Bernardino, Riverside, Los Angeles, Orange, and Santa Barbara Counties. (Phillips 1999). Further infestations have been reported as recently as October 2000, in Sacramento, Butte, and Contra Costa counties. In November 2000, it reached the vineyards of Sonoma County.(CA 2000). Homalodisca coagulata will continue to spread throughout all of California's agricultural regions.
 

Natural History:
Homalodisca coagulata adults live for only two months. They lay their eggs under the epidermis of host plants. These egg clusters appear as small fluid-filled sacs on the leaves. The eggs hatch within two weeks. Nymphs are small and white. They feed upon the stems of the host plant, destroying it even further. Nymphs under go four molting phases before maturity. Two egg laying phases occur each year in July/August and February/March. (CDFA 2000)

Homalodisca coagulata prefer thick leafy plants. It's original habitat was the low scrub of the Southwest desert areas, but it has easily adapted to the lush agricultural areas of California.  orchards and vineyards are now the insects' habitat of choice. The long, evenly spaced rows of continuous vegetation have provided a "highway system" that has facilitated the rapid infestation of sharpshooters throughout the Central Valley.
 
Evolution:
Insects are among the oldest life forms on the planet. The first arthropods appeared in the Paleozois era, as evidenced by the fossils found in the Burgess Shale of Northern Canada. The Burgess Shale fauna were a varied group axhibiting many variations on the insect from theat survives today. (Briggs et al 1994). Some of these creatures survived mass extinction events at the end of the Cambrian. These went on to evolve into the much larged arthropods of the Mesozoic. Large flying insects appeared during the Permian period. A rapid radiation of all types of arthropods occurred through the Jurassic. Unlike the dinosaurs of the Mesozoic, insects survived the mass extinction event of the Cretaceous and have gone on to become the most populous and widespread fauna on the planet.
 
Other interesting issues:
Homaladisca coagulata has been identified as a serious threat to California's viticultural regions because it is a known vector of Pierce's Disease, the plant pathogenic bacterium Xylella fastidiosa. Pierce's Disease, once injected by a sharpshooter into a plant, will cause a rapid die-back of foliage and eventual death of the entire plant. Because this could mean disaster to the wine industry early detection of Homalodisca coagulata is very important. Only one biological control has been identified. Gonatocerus ashmeadi Girault is a parasite that attacks the eggs of Homalodisca coagulata. (Phillips 1999). Other measure to avoid complete infestation include spraying vineyards and surrounding agricultural areas, especially citrus. Pierce's Disease also causes Almond Leaf Scorch Disease and Oleander Scorch. Because oleander is found in 20% of all home gardens in California, and is used extesively as an ornamental windbreak along all major highways, the destruction of this plant is of real concern to CalTrans and other public agencies.

Research to prevent the oncoming disaster that Homalodisca coagulata will bring is ongoing at the University of California Riverside, Davis, and Berkeley. Methods for early detection, as well as strategies for control and eradication of this pest are a high priority in the Agri-research field. The American Vineyard Foundation has declared the Glassy-winged Sharpshooter as "Public Enemy # 1"
 
Bibliography
Borror, Donald J., and Richard E. White.1970. A Field Guide to the Insects. Boston., Massachusetts. Houghton Mifflin Company.

Briggs, Derek E.G., DouglasH. Erwin, and Frederick J. Collier. 1994. The Fossils of the Burgess Shale. Washington and London. SmithsonianInstitution Press.

California Department of Food and Agriculture. 4 August 2000. "Distribution Of Glassy-winged Sharpshooter". [Online] Available: California Homepage. [Online] Available: http://www.cal.gov

Phillips, Phil A. 1999. TheGlassy-winged Sharpshooter :A Serious New Vector for Pierce's Disease". University of California at Santa Barbara. [Online]Available: http://ucceventura.xlrn.ucsb.edu/IPM/Publications/

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