Technical Abstract: After glassy-winged sharpshooter (GWSS), Homalodisca vitripennis, arrived in California, it was believed that the insect would establish throughout much of the northern agricultural production areas. However, GWSS 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, thereby reducing its ability to survive cold winters. We plan to verify the impact of cool temperatures on GWSS adults by exposing them to a regime of seasonal temperatures (within temperature cabinets) that reflect some of the marginal areas where we expect GWSS to poorly survive California winters. The goal of the study would be to determine the ability of GWSS adults to survive winter conditions around the state by subjecting GWSS adults to low temperatures with daily temperatures below 10°C and nightly temperatures above 0°C. Using temperature records to calculate numbers of cooling degree days, we plan to construct 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. If successful, post-winter GWSS survival maps could be produced each spring (e.g., April) that would provide estimates of where GWSS populations should be absent or minimal because of winter conditions.