Visual orientation of Pissodes strobi Peck (Coleoptera: Curculionidae) in relation to host selection behaviour

Abstract

Visual orientation plays an important role in short-range host selection by Pissodes strobi. Results of laboratory orientation experiments suggest both sexes of P. strobi are predisposed to attack vertical or near-vertical Sitka spruce leaders that are about 3 cm in silhouette width and above-average in length. In addition, these data suggest that female weevils may possess greater visual discrimination than males. Field data confirm that both sexes of P. strobi select only the longer, larger diameter host leaders from among the population of leaders available. For brood hosts reattacked the 2nd year, stepwise discriminant analysis was performed to select that combination of host characteristics which best distinguished weevilled from unattacked lateral branches in host crowns. The most efficient host property in this regard was lateral branch length. Of decreasing importance were angular deviation from the vertical and lateral branch diameter measured at the midpoint. The data support the hypothesis that reattack of brood hosts is accomplished by resident weevil populations which fail to disperse after overwintering.