Glassy-winged sharpshooter (Homalodisca vitripennis) oviposition effects on foliar grapevine and red-tipped photinia terpenoid levels

The glassy-winged sharpshooter (GWSS), Homalodisca vitripennis (Germar) (Hemiptera: Cicadellidae), is an important vector of Xylella fastidiosa, the bacterium that causes Pierce's disease of grapevine and is a threat to grape production throughout the United States.  Female GWSS deposit egg masses beneath the epidermis layer on the abaxial side of leaves of many host plants.  Host plants respond to GWSS oviposition by releasing volatile chemicals that attract mymarid parasitoids to the egg masses thus interrupting GWSS reproduction. Previously, greater concentrations of two terpenoids were emitted from GWSS-infested leaves of grapevine compared to non-infested leaves.  This study examined terpenoid concentrations present within leaves of GWSS egg-infested grapevines and red-tipped photinia and compared with levels present in non-infested plants. This was done to directly observe the accumulation of terpenoid compounds within tissues prior to emission from each of these host plants, and to discover differences between grapevine and photinia defense responses. Since in previous studies parasitoids were more responsive to GWSS infested red-tipped photinia leaves than grapevines leaves, findings should determine which particular compounds or blend of compounds unique to photinia allow it to better defend itself than grapevine against GWSS.