Identifying Key Predators of the Various Glassy - Winged Sharpshooter Lifestages

Using glassy-winged sharpshooter (GWSS) egg-specific monoclonal antibody (MAb) and GWSS-specific genetic markers that we previously developed and optimized, the guts of field-collected predators were screened for the presence of GWSS remains. We have examined the guts of over 700 generalist predators and our analyses revealed that frequent predators of the GWSS include spiders, assassin bugs, lacewings and praying mantis. INTRODUCTION Effective control of GWSS will require an area-wide integrated pest management approach (AW-IPM). A major component of Area-wide-Integrated Pest Management is the exploitation of the pest’s natural enemies, which, when utilized to their greatest potential, can increase the effectiveness of other control tactics. Very little information exists on GWSS’s predaceous natural enemies. Identifying the impact of predators can be challenging as they are usually small, elusive, nocturnal or cryptic. Direct visual field observations of predation are rare and often difficult to obtain. While predation studies using enclosures can provide some indication of predator impact, it fails to recreate natural conditions and can result in an overestimation of predation. A more valid method to qualitatively identify predators of key pests in nature is by the molecular analysis of predator gut contents for pest remains (reviewed in Sheppard and Harwood 2005). The state-of-the-art predator stomach content analyses include both MAb-based enzyme-linked immunosorbant assays (ELISA), which detect prey-specific proteins (Hagler et al. 1994ab, Schenk and Bacher 2004), and polymerase chain reaction (PCR)-based assays, which detect prey-specific DNA (Zaidi et al. 1999, Agustí et al. 2003). While DNA-based approaches reveal the prey identity at the species-level, they are unable to indicate which prey life stage is consumed. In contrast, pest-specific and life stage-specific MAbs can target a particular life stage of a given species, providing a higher level of precision to document predation (Hagler and Naranjo 1996). Combining both assays can provide a powerful tool to study predation on the GWSS. To this end, genetic markers were designed using the cytochrome oxidase gene subunit I (COI) to detect and amplify a GWSS-specific fragment (de León et al. 2004, de León et al. submitted), and a GWSS-egg specific MAb was developed to detect GWSS egg-specific protein (Hagler et al. 2002, Fournier et al. 2004, Fournier et al. submitted). OBJECTIVE The main objective of this research is to identify the key predators of the different life stages of GWSS. More specifically, our aim is to determine the proportion of predators feeding on the various GWSS life stages in nature. Using GWSS-specific ELISA and PCR assays, we examined the guts of several hundred field-collected generalist predators. Results obtained from this research will aid in evaluating the efficacy of generalist predators for a conservation or an inundative biological control program. RESULTS From 2002 to 2004, generalist arthropod predators were collected from various species of shrubs and ornamental trees located in 20 sites in urban areas of Bakersfield, California. For each group of predators, lab trials were conducted to generate negative controls (i.e. individuals with no GWSS remains in their guts) and positive controls (i.e. individuals fed GWSS). Frozen specimens were shipped to USDA-ARS, Phoenix and screened by a GWSS egg-specific ELISA and a GWSS-specific PCR assay. All individuals were first homogenized in phosphate buffered saline and then aliquoted into two Eppendorf tubes in order to perform the two different assays (ELISA and PCR). For PCR assays, DNA was extracted using DNeasy tissue kit (Qiagen, protocol for insects). DNA samples were then subjected to the primer set HcCOI (forward 5’-