Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/29/2013
Publication Date: 2/1/2014
Citation: Sisterson, M.S. 2014. Evaluation of a method to quantify glassy-winged sharpshooter (Hemiptera: Cicadellidae) egg maturation during a feeding assay. Journal of Economic Entomology. 107:206-214. Interpretive Summary: Insects in the suborder Auchenorrhyncha transmit a wide range of economically important plant pathogens. Epidemiological models indicate that vector abundance is a key factor affecting rate of pathogen spread. As vector population growth is a function of the number of eggs produced per female, a complete understanding of the egg maturation dynamics of insects that transmit plant pathogens may suggest novel targets for control. Despite this, the egg maturation dynamics of insects in the sub-order Auchenorrhyncha are poorly understood. The glassy-winged sharpshooter is a member of the Auchenorrhyncha that is capable of transmitting the bacterial pathogen Xylella fastidiosa, the causal agent of Pierce’s disease of grapevine. Identification of dietary components that contribute to glassy-winged sharpshooter egg maturation is hampered by difficulties associated with estimating the number of mature eggs produced by females during feeding assays. Estimates of the number of mature eggs produced by glassy-winged sharpshooter females during feeding assays improve as variability in the number of mature eggs carried by females entering the assay declines. Accordingly, a method to reduce variation in the number of mature eggs carried by females entering a feeding assay was assessed. This study determined that providing females with an egg laying period on sorghum prior to the feeding assay reduced variation in the number of mature eggs carried by females entering the assay thereby improving estimates of egg maturation during the assay. Providing females with an egg laying period on sorghum reduced variation in the number of mature eggs carried by females entering the feeding assay because females readily deposited eggs on sorghum, but did not produce new mature eggs when feeding on sorghum. Improved methodology for estimating rates of egg maturation will enable design of studies aimed at identifying nutritional factors affecting egg maturation by the glassy-winged sharpshooter.
Technical Abstract: Methods to improve an assay relating adult feeding to egg maturation by the glassy-winged sharpshooter (Hemiptera: Cicadellidae) were evaluated. The assay consisted of confining adult females to cowpea stems in parafilm enclosures and quantifying adult feeding and egg maturation. Adult feeding was quantified by measuring excreta production. Egg maturation during the assay was estimated by taking the difference between female egg load (number of mature eggs carried by a female) at the end of the assay (determined by dissection) and mean egg load of a subset of females dissected at the start of the assay. Estimates of egg maturation using this approach improve as variability in egg loads of females entering the assay decline. Accordingly, a method to reduce variation in egg loads of females entering the assay and subsequent effects on clarity of the relationship between feeding and egg maturation were assessed. Specifically, field collected females were divided into two groups. One group was placed directly into the assay. The other group was given an oviposition period on sorghum prior to being moved into the assay. Dissection of a subset of females from each group prior to the start of the assay determined that variance in egg load was significantly reduced for females provided an oviposition period on sorghum relative to field collected females. Females provided an oviposition period on sorghum had reduced variance in egg loads relative to field collected females because sorghum was acceptable for oviposition, but provided poor nutrition for maturing new eggs. There was a significant positive relationship between feeding (as measured by excreta production) and egg maturation for females provided an oviposition period on sorghum prior to the assay, but no relationship between feeding and egg maturation for females placed directly into the assay. Accordingly, reducing variation in egg loads of females entering the assay provided a clearer assessment of the relationship of feeding with egg maturation.