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Assessing the Post-Winter Threat of Glassy-winged Sharpshooter Populations

Johnson, Marshall W., Lynn-Patterson, Kris, Sisterson, Mark, Groves, Russell
Proceedings of the Pierce's Disease Research Symposium 2008 pp. 22-27
Homalodisca vitripennis, geographical distribution, insect vectors, vector-borne diseases, insect pests, overwintering, temperature, mortality, cold tolerance, feeding behavior, climatic factors, California
Glassy-winged sharpshooter (GWSS), Homalodisca vitripennis, appears to be limited to discrete regions within the San Joaquin Valley where winter temperatures are mild and the temperature rarely drops below freezing. Prior research indicates that GWSS adults cannot feed at maximum daily temperatures below 50°F (= 10°C), thereby reducing its ability to survive cold winters. We verified the impact of cool temperatures on GWSS adults by exposing them to a regime of seasonal temperatures (within temperature cabinets) that reflect a variety of areas within the state. As expected, mortality rates varied greatly among sites tested, and it appears that mortality is related to both length of exposure as well as intensity of exposure (i.e., amount of cold endured). Using temperature records to calculate numbers of cooling degree days, we constructed ten GIS maps to delineate areas where post-winter GWSS mortality should be substantial, thereby providing a tool to estimate the springtime GWSS threat to different regions. However, estimates of post-winter GWSS mortalities were usually smaller (< 90%) than expected across much of the agricultural production areas of the Central Valley.