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Submitted to: CDFA Pierce's Disease Control Program Research Symposium
Publication Type: Abstract Only Publication Acceptance Date: 11/1/2014 Publication Date: 12/3/2014 Citation: Wallis, C.M., Krugner, R. 2014. Glassy-winged sharpshooter oviposition effects on photinia volatile chemistry with implications on egg parasitoid effectiveness. CDFA Pierce's Disease Research Progress Reports. p. 256. Interpretive Summary: Technical Abstract: An effective way to limit incidence of Pierce’s disease of grapevine is to reduce populations of glassy-winged sharpshooter (GWSS), Homalodisca vitripennis (Germar) (Hemiptera: Cicadellidae), which transmit the causal bacterium, Xylella fastidiosa. One strategy is to utilize egg parasitoids such as Gonatocerus ashmeadi Girault (Hymenoptera: Mymaridae) to consume GWSS eggs. However, greater knowledge is needed about how parasitoids find hosts to improve effectiveness of control. Previous work showed that G. ashmeadi preferred plants with egg masses to those without, with greater preference for red-tip photinia (Photinia x fraseri) bearing egg masses than egg-mass colonized grapevine or citrus (Krugner et al. 2008). Likewise, G. ashmeadi was preferentially attracted to mixes of two grapevine volatile compounds, ß-ocimene and a-farnesene, in choice assays (Krugner et al. 2014). Concentrations of both compounds were elevated in volatile profiles taken from egg-infested grapevines compared with non-infested controls (Krugner et al. 2014). Photinias are commonly planted throughout California as ornamental plants and are used by GWSS for oviposition. Therefore, the current study examined GWSS egg-infested photinia to observe if additional parasitoid-attracting compounds were present in that host compared to grapevines. To this end, three to six photinia plants each were either exposed to egg-laying GWSS females or left non-exposed for three days in cages in a containment greenhouse at USDA-ARS in Parlier, CA. After the three-day oviposition period, leaves were collected from non-infested and egg-mass infested grapevines, the tissue pulverized and extracted in methyl tert-butyl ether, and volatile terpenoids were analyzed using gas chromatography-mass spectrometry. The experiment was replicated in full three times. Of over 30 compounds analyzed, six were observed to occur at significantly greater levels in egg-infested leaves than in leaves from control plants. These were tentatively identified as ß-ocimene, a-pinene, delta-3-carene, linalool, a-farnesene, and an additional farnesene enantiomer. Once all compounds are definitively identified, they will be tested for relative attractiveness to female parasitoids in wind tunnels and/or Y-tube olfactometry. These findings could be utilized in development of lures for monitoring egg parasitoid populations and biocontrol effectiveness. |
