Technical Abstract: Four newly discovered viral pathogens in leafhopper vectors of Pierce¿s disease of grapes, have been shown to replicate in sharpshooter leafhoppers; the glassy-winged sharpshooter, GWSS, Homalodisca vitripennis, and Oncometopia nigricans (Hemiptera: Cicadellidae). The viruses were classified as members of the Reoviridae, Phytoreoviridae, Rhabdoviridae, and Dicistroviridae. Leafhoppers appear to be permissive to RNA viruses (both dsRNA and ssRNA). Of these the virus genome of Homalodisca virus-1, was sequenced, and the path of infection into the leafhopper was determined to be through ingestion and infection through the midgut tissues. These viral pathogens occur naturally in the wild and have potential as a biological control agents for the management of leafhoppers. Currently viral biological control agents of leafhoppers are lacking. The GWSS is considered the main vector of plant diseases such as Pierce¿s disease of grapes. But all leafhoppers tested so far have shown the ability to spread the bacterium, Xylella fastidiosa , which causes these `Scorch¿-like diseases. These leafhopper-infecting viruses were shown to be infecting field populations of GWSS across several different states from Florida to California. Infected adult GWSS were dissected and examined. Comparative analysis of sequences isolated directly from the salivary glands and midguts showed high levels of the virus in the midgut tissues. Examination by electron microscopy supports the hypothesis that the midgut tissues act as the entry and replication sites for some of the single-stranded RNA viruses. While viruses serve as naturally-occurring biological control agents, a cost/benefit analyses is being conducted to determine an efficient means of virus mass production and application strategies to reduce leafhopper pests. Population suppression strategies, such as this may reduce the transmission of disease causing pathogens, like the bacterium, Xylella fastidiosa.