Submitted to: Environmental Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/23/2017
Publication Date: 3/6/2017
Citation: Sisterson, M.S., Wallis, C.M., Stenger, D.C. 2017. Effects of xylem-sap composition on glassy-winged sharpshooter egg maturation on high and low quality host plants. Environmental Entomology. 46:299-310.
Interpretive Summary: Epidemics of Pierce’s disease in Southern California and the Southern San Joaquin Valley of California during the late 1990’s were a result of invasion of California by an exotic vector, the glassy-winged sharpshooter. To limit economic damage caused by the glassy-winged sharpshooter, an area-wide suppression program was initiated in the early 2000’s and has been maintained for over a decade. As the area-wide suppression program relies on use of chemical insecticides, environmentally friendly and sustainable management approaches are needed. Glassy-winged sharpshooter egg production is known to be affected by adult diet, but dietary components contributing to egg production have yet to be identified. As glassy-winged sharpshooters consume xylem-sap, concentrations of amino acids in xylem-sap of a high and low quality host plant were compared. Concentrations of 17 of 19 amino acids were greater in the high quality host plant than in the low quality host plant. Thus, glassy-winged sharpshooters held on the low quality host plant may have consumed less xylem-sap than glassy-winged sharpshooters held on the high quality host plant due to perceived lower quality. Further, females held on the low quality host plant produced fewer eggs than females held on the high quality host plant due to the lower nutritional return per unit volume of xylem-sap consumed. Identification of dietary components that contribute to glassy-winged sharpshooter egg production will aid in identifying host plant species that limit glassy-winged sharpshooter population growth.
Technical Abstract: Glassy-winged sharpshooters must feed as adults to produce mature eggs. Cowpea and sunflower are both readily accepted by the glassy-winged sharpshooter for feeding, but egg production on sunflower was reported to be lower than egg production on cowpea. To better understand the role of adult diet in egg production, effects of xylem-sap chemistry on glassy-winged sharpshooter egg maturation was compared for females confined to cowpea and sunflower. Females confined to cowpea consumed more xylem-sap (as measured by excreta production) than females held on sunflower. In response, females held on cowpea produced more eggs, had heavier bodies, and greater lipid content than females held on sunflower. Analysis of cowpea and sunflower xylem-sap found that 17 of 19 amino acids were consistently more concentrated in cowpea xylem-sap than in sunflower xylem-sap. Thus, decreased consumption of sunflower xylem-sap was likely due to perceived lower quality, with decreased egg production due to a combination of decreased feeding and lower return per unit volume of xylem-sap consumed. Principal component analyses indicated that concentrations of amino acids within plant species were correlated. Proportional quantities of amino acids within plant species also were correlated. For females held on cowpea, test date and principal component 2 based on proportional quantities of amino acids explained 22% of variance in glassy-winged sharpshooter feeding. Test date, volume of excreta produced per female, and principal component 2 based on concentrations explained 62% of variance in egg load weight of females held on cowpea. Principal component analyses aided in identifying groups of covarying amino acids that were correlated with egg production by females held on cowpea, although determining which of the covarying xylem-sap components are key for egg production will require additional testing and novel methodology.