Sampling methods and seasonal phenology of Sphenophorus venatus confluens Chittenden (Coleoptera: Curculionidae) in orchardgrass (Dactylis glomerata L.)

Sampling methods and seasonal phenology of the billbug pest, Sphenophorus venatus confluens Chittenden (Coleoptera: Curculionidae), were studied in unburned orchardgrass (Dactylis glomerata L.) seed production fields in western Oregon to evaluate the potential for improving management of this pest by shifting the timing of control measures from the spring to the fall for enhanced pest management. The occurrence and timing of life stages of the univoltine S. venatus confluens varied little from that reported previously for fields annually burned after harvest to remove residues of straw and chaff. New generation adults became active in October without the previously reported stimulus of postharvest, open field burns. In sampling for larvae, pupae, and adults, the relative net precision (RNP) of a 9-cm diameter circular soil sample unit was over twice that of either a 16-cm or 26-cm diameter sample unit. Monitoring life stages of billbugs using the 9-cm soil sample unit and pitfall traps to determine adult activity in the fall should improve management of this serious pest in unburned orchardgrass fields. We conclude that management of this pest can be enhanced by using control measures in the fall rather than the current practice of spring management.