Effects of energy reserves and diet on glassy-winged sharpshooter egg maturation

Authors: Sisterson, Mark; Krugner, Rodrigo; Wallis, Christopher; Stenger, Drake

Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/16/2017
Publication Date: 2/9/2018
Citation: Sisterson, M.S., Krugner, R., Wallis, C.M., Stenger, D.C. 2018. Effects of energy reserves and diet on glassy-winged sharpshooter egg maturation. Journal of Economic Entomology. 111:159-169.

Interpretive Summary: Epidemics of Pierce’s disease of grapevine in California were due to introduction of the invasive glassy-winged sharpshooter. To reduce levels of Pierce’s disease, a glassy-winged sharpshooter area-wide suppression program was initiated in the early 2000’s. However, sharpshooter numbers have increased in some locations, with evidence that sharpshooters may have evolved resistance to commonly applied insecticides. Accordingly, control strategies that do not rely on insecticides are needed. To understand regulation of egg production in the glassy-winged sharpshooter, effects of energy reserves and diet on glassy-winged sharpshooter egg maturation were studied. Females with large energy reserves produced more eggs over a six-day feeding period than females with small energy reserves. In addition, females held on host plants with high amino acid concentrations produced more eggs than females held on plants with low amino acid concentrations. These results improve basic understanding of how glassy-winged sharpshooter females use incoming and stored energetic reserves to produce mature eggs. Identification of factors contributing to glassy-winged sharpshooter egg production will improve ability to forecast population growth rates and may aid in identifying novel targets for pest control.

Technical Abstract: Effects of stored energy and diet quality on glassy-winged sharpshooter egg maturation were evaluated. To evaluate effects of diet quality on egg maturation, egg load weights of females at the end of a 6-day feeding period on cowpea or grapevine were compared. To estimate energy reserves available at the beginning of feeding assays, residuals from a regression of wet weight (determined for live insects) on size (hind tibia length x head capsule width) were used. Females with a positive residual wet weight were heavy for their size, and females with a negative residual wet weight were light for their size. Analysis of a subset of females, sacrificed at the beginning of feeding assays, demonstrated that residual wet weight was positively associated with insect lipid content and egg load weight. Accordingly, females with a positive residual wet weight were more likely to have higher lipid content and carry more mature eggs than females with a negative residual wet weight. Females with a positive residual wet weight matured more eggs over a 6-day feeding period on cowpea and grapevine than females with a negative residual wet weight, demonstrating the utility of residual wet weight as a covariate to control for differences in available energy reserves and presence of mature eggs. Females held on cowpea produced more excreta and more eggs than females held on grapevine. Comparison of cowpea and grapevine xylem-sap found that 9 amino acids were consistently more concentrated in cowpea xylem-sap than in grapevine xylem-sap, whereas concentrations of 4 organic acids were consistently higher in grapevine xylem-sap than in cowpea xylem-sap. Thus, differences in insect performance were associated with quantifiable differences in xylem-sap composition between the two plant species.