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Title: Distribution of glassy-winged sharpshooter and threecornered alfalfa hopper on plant hosts in the San Joaquin valley

item Sisterson, Mark

Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/22/2010
Publication Date: 8/1/2010
Citation: Wistrom, C., Sisterson, M.S., Pryor, M., Hashim, J., Daane, K.M. 2010. Distribution of glassy-winged sharpshooter and threecornered alfalfa hopper on plant hosts in the San Joaquin valley. Journal of Economic Entomology. 103(4):1051-1059.

Interpretive Summary: Introduction of the glassy-winged sharpshooter (Homalodisca vitripennis) into California resulted in two epidemics of Pierce’s disease. This disease is caused by the bacterial pathogen Xylella fastidiosa that is vectored by xylem feeding insects. In response to these epidemics, an area-wide suppression program was initiated to reduce glassy-winged sharpshooter populations. This program relies on treating citrus, a key overwintering host of the glassy-winged sharpshooter. As the glassy-winged sharpshooter has a broad host-range, it has persisted in area-wide treatment zones on non-citrus hosts. We surveyed non-citrus hosts within an area-wide treatment zone to determine which plants play an important role in maintaining glassy-winged sharpshooter populations. In conjunction, we also surveyed populations of the three cornered alfalfa hopper (Spissistilus festinus), an insect whose status as a vector of X. fastidiosa is currently unknown. Glassy-winged sharpshooter persisted at all sites surveyed and had high numbers on eucalyptus and jojoba. Abundance of three cornered alfalfa hopper at the same sites was similar to that of glassy-winged sharpshooter, but lower than what is typically observed in their preferred habitat, alfalfa. Finally, transmission tests with the three cornered alfalfa hopper were conducted to determine if it vectors X. fastidiosa. These tests suggest that it is not a vector. This research will aid in determining which plant hosts should be targeted for treatment in glassy-winged sharpshooter infested areas.

Technical Abstract: Homalodisca vitripennis Germar and Spissistilus festinus Say populations were surveyed bimonthly for 14 months in Kern County at five agricultural sites made up of a variety of potential host plants. Additionally, S. festinus populations were surveyed in four alfalfa fields in Kern and Tulare Counties. Insects were collected by beat-sweeps and sticky traps. Data on host plant condition, phenology, and ground cover was collected at the five agricultural sites, whereas data on mowing and insecticide use was collected at the four alfalfa sites. Populations of both insects persisted at the five agricultural locations despite insecticide applications applied as part of an area-wide management program. Plants colonized in these areas included eucalyptus, jojoba, and citrus. Populations of S. festinus were much greater in collections from alfalfa fields than in collections from the five agricultural sites. No H. vitripennis were collected from alfalfa fields. Insects collected from the five mixed agricultural sites were negative for presence of X. fastidiosa. As the vector status of S. festinus remains unresolved, greenhouse transmission tests were conducted. Such tests failed to document acquisition or transmission of X. fastidiosa by S. festinus using infected grape as an acquisition source and grape, almond, and alfalfa as inoculation hosts. Recommendations for vector control, vegetation management, and targeted monitoring to reduce insect populations and inoculum potential are discussed.