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Submitted to: Meeting Abstract
Publication Type: Abstract Only Publication Acceptance Date: 11/21/2016 Publication Date: 12/2/2016 Citation: Wallis, C.M., Krugner, R. 2016. Grapevines respond to glassy-winged sharpshooter (Homalodisca vitripennis) oviposition by increasing local and systemic terpenoid levels. Meeting Abstract. p. 238. Interpretive Summary: Technical Abstract: Grapevines (Vitis vinifera) have been observed to respond to oviposition by glassy-winged sharpshooters [Homalodisca vitripennis (Germar)(Hemiptera: Cicadellidae)] by producing volatile compounds that attract egg parasitoids such as Gonatocerus ashmeadi Girault (Hymenoptera: Mymaridae). Recent work also has shown that two particular volatiles, the terpenoids ß-ocimene and a-farnesene, were present in greater amounts in air space around egg mass-infested grapevines versus non-infested grapevines, and these compounds were attractive to G. ashmeadi in olfactometry studies. However, methodologies to trap and sample volatiles from air around plants are less sensitive than determining accumulation within plant foliage. This study quantified terpenoids, which are defense-associated volatile compounds, within leaves of non-infested plants and those exposed to egg-laying female sharpshooters. Infested grapevines had leaves with and without egg masses taken to examine both localized and systemic, plant-wide changes in terpenoid levels. Total terpenoid levels were increased in leaves collected from infested plants, regardless if the leaves had egg masses present. A total of 13 monoterpenoids, including ocimene isomers, and nine sesquiterpenoids, including farnesene isomers, were present in greater amounts in leaves with egg masses than leaves without eggs. Leaves from infested plants without egg masses did not have significantly greater monoterpenoid levels than controls, but there was greater levels of three individual sesquiterpenoids in such leaves than controls. Of all the terpenoids, only ß-ocimene appeared to also be present in greater amounts in leaves with egg masses than leaves without egg masses taken from infested plants. These results support previous findings that ocimene and farnesene produced by grapevines attract egg parasitoids. However, additional volatile compounds also were upregulated and could be involved in attraction of natural predators or possess other roles in host defense against sharpshooters. Therefore, future studies should focus on observing terpenoid roles in providing grapevine resistance to sharpshooters and similar insects. |
