Submitted to: CDFA Pierce's Disease Control Program Research Symposium
Publication Type: Proceedings
Publication Acceptance Date: 10/29/2008
Publication Date: 12/15/2008
Citation: Johnson, M.W., Lynn-Patterson, K., Sisterson, M.S., Groves, R. 2008. Assessing the post-winter threat of glassy-winged sharpshooter populations. In: Proceedings of the CDFA Pierce's Disease Control Program Research Symposium, December 15-17, 2008, San Diego, California. p. 22-27.
Interpretive Summary: The glassy-winged sharpshooter was introduced into California sometime in the late 1980’s. This insect is viewed as a major threat to grape production in California due to its ability to vector Xylella fastidiosa, the causal agents of Pierce’s disease of grape. The range of the glassy-winged sharpshooter is currently limited to portions of southern California and portions of the southern San Joaquin Valley. These areas have mild winter temperatures that rarely drop below freezing. Prior research indicates that glassy-winged sharpshooter adults do not feed when maximum daily temperatures are below 50°F (= 10°C). Consequently, when temperatures fall below this threshold for sustained periods, glassy-winged sharpshooter populations are expected to experience significant mortality. We used programmable temperature cabinets to determine effects of different overwintering temperature regimes on glassy-winged sharpshooter survival. As expected, mortality rates varied greatly among temperature regimes, and it appears that mortality is related to both length of exposure to cold temperatures as well as intensity of exposure. This information, combined with previous laboratory studies was used to develop a cooling degree day model. The model was used to construct Geographic Information Systems (GIS) maps to delineate areas where glassy-winged sharpshooter overwinter mortality should be substantial. This research will facilitate identification of uninfested portions of California at greatest risk for establishment of new glassy-winged sharpshooter populations.
Technical Abstract: Glassy-winged sharpshooter (GWSS), Homalodisca vitripennis, appears to be limited to discrete regions within the San Joaquin Valley where winter temperatures are mild and rarely drop below freezing. Prior research indicates that GWSS adults cannot feed when maximum daily temperatures are below 50°F (= 10°C), thereby contributing to winter mortality. We verified the impact of cool temperatures on GWSS adults by exposing them to a regime of seasonal temperatures (within temperature cabinets) approximating various climate regimes in California. As expected, mortality rates varied greatly among temperature regimes tested, and it appears that mortality is related to both length of exposure as well as intensity of exposure. Using temperature records to calculate numbers of cooling degree days, we constructed GIS maps to delineate areas where winter GWSS mortality should be substantial, thereby providing a tool to predict regions where GWSS cannot survive the winter. However, estimated winter GWSS mortality was smaller (< 90%) than expected across much of the agricultural production areas of the Central Valley.