Submitted to: CDFA Pierce's Disease Control Program Research Symposium
Publication Type: Abstract Only
Publication Acceptance Date: 10/24/2013
Publication Date: 12/16/2013
Citation: Sisterson, M.S. 2013. A method to quantify glassy-winged sharpshooter egg maturation. In: Proceedings of the Pierce's Disease Research Symposium, December 16-18, 2013, Sacramento, California. pp. 12.
Technical Abstract: To identify factors affecting glassy-winged sharpshooter egg production, a method to accurately estimate the number of mature eggs produced during a short-term assay is needed. Egg production is typically quantified by determining the number of eggs deposited during the assay plus the number of mature eggs carried by the female at end of the assay (determined by dissection). However, this approach ignores confounding effects of variation in number of mature eggs carried by females entering an assay. Dissection of field-collected females indicates that egg loads of reproductively active females are variable (range 0 to 37 eggs; Sisterson 2008). If the number of eggs carried by females entering an assay is variable, subsequent estimates of egg production during the assay will be inaccurate. Poor estimates of egg production during assays increase risk of making a Type II error (failure to reject a false null hypothesis). To address this issue, a pre-treatment designed to reduce variance in the number of eggs carried by females entering a feeding assay was evaluated. The pre-treatment consisted of providing females with a four-day oviposition period on sorghum. An oviposition period on sorghum was expected to reduce mean and variance in the number of eggs carried by females as previous tests documented that females readily deposit eggs on sorghum, but do not mature eggs when feeding on sorghum (Sisterson 2012). To determine if an oviposition period on sorghum reduced mean and variance in the number of eggs carried by a group of females, field-collected females were split into two groups. The control group was dissected immediately to determine the number of eggs carried by each female. The pre-treatment group was provided with a 4-day oviposition period on sorghum prior to dissection. The mean number of eggs carried by females in the pre-treatment group was 63% lower than for females in the control group. Similarly, the standard deviation in the number of eggs carried by females in the pre-treatment group was reduced by 44% compared to females in the control group. To demonstrate the importance of reducing variance in the number of eggs carried by females entering a feeding assay, results from feeding assays using females directly from the field were compared to results of feeding assays using females exposed to the pre-treatment. The feeding assay consisted of confining females to cowpea stems in parafilm enclosures for six days. Feeding was quantified during the assay by measuring excreta production. As females typically do not deposit eggs on stems, females were dissected at the end of six days to quantify egg production. A significant relationship between feeding (as measured by excreta production) and egg production was observed for females exposed to the pre-treatment before the feeding assay (P = 0.04), but was not observed for females placed directly into the feeding assay (P = 0.35). Thus, reducing mean and variance in the number of eggs carried by females entering the feeding assay resulted in detection of a significant positive relationship between feeding and egg production that otherwise would not have been observed. Use of the methodology proposed here will aid in completion of more in-depth studies designed to identify factors affecting glassy-winged sharpshooter egg production.