Behavioral response of grape root borer (Lepidoptera: Sesiidae) larvae to grape root stimuli suggests attraction to host-specific volatiles

Grape root borer, Vitacea polistiformis (Harris) is an economically important, oligophagous pest of grapevines in parts of the eastern United States. Neonates hatch from eggs deposited above ground and burrow into the soil to find and feed on grape roots. Food-finding by edaphic, oligophagous insects is often facilitated or mediated by their response to secondary plant metabolites. Previous studies demonstrated that V. polistiformis larvae responded positively to filter paper discs treated with grape root extracts, although the bioassay protocol did not enable determination of whether the response occurred before or after contacting the stimulus source.  The objective of this study was to measure the response of larvae to grape root stimuli from which they were physically isolated. The bioassay consisted of small (50 × 9 mm) Petri dishes containing two glass vials suspended from opposing quadrants on the dish bottom. One or more neonates (< 2-hr-old) were released at the center of each dish, which was then covered with a ventilated lid and held under dark and humid conditions.  The number of larvae recorded in each vial was recorded after 1-hr in single and paired stimulus bioassays using grape root extracts, excised pieces of grape root, and non-host (apple) roots. Larvae responded to grape root stimuli, suggesting the presence of volatile, behaviorally-active compounds associated with grape roots.