Food-finding by larval grape root borer, Vitacea polistiformis (Lepidoptera: Sesiidae) in a soil column bioassay

Grape root borer is an oligophagous pest of grapevines in parts of the eastern USA. After hatching from eggs deposited on the above-ground parts of grape vines and other plants, neonates must burrow through the soil to locate grape roots, on which they feed. As an extension of my research on their behavioral response to grape root stimuli in Petri dish bioassays, I developed a soil column bioassay to evaluate larval grape root borer food-finding under conditions that more closely simulated those in nature. We evaluated the effect of a food source on larval recovery in vertical columns, the effect of vertical column length on larval recovery, and larval movement in a horizontal column. Soil columns consisted of PVC pipes filled with sifted soil at 25% water content. An adaptor and pipe cap at the bottom of vertical columns or at both ends of horizontal columns contained pieces of grape root and/or a sticky disc to recover larvae. A single egg from which larval emergence was imminent was placed in a small a dish at the top of vertical columns or in a hole at the mid-point of horizontal columns. The number of larvae recovered from the end(s) of columns were recorded. The presence of food did not influence the number of larvae recovered. Larvae were recovered from vertical columns up to 120 cm in length and from both ends of horizontal columns. These results are discussed in relation to planned future studies of food-finding by larval grape root borer.