An effective strategy for trapping Douglas-fir beetle, Dendroctonus pseudotsugae (Col., Scolytidae) using combinations of unbaited and pheromone baited funnel traps

Experiments were conducted to confirm and quantify earlier observations that unbaited funnel traps in conjunction with pheromone baited funnel traps may substantially increase trap catches of Douglas-fir beetles, Dendroctonus pseudotsugae. In 12 replicates of one of these experiments during 1998 and 1999, the catches of a single baited control trap were compared to those of a set of four traps where the central trap was baited and a ring of three traps, 1 m from the central trap arranged in a star configuration, were unbaited. In the second experiment conducted during 1999, a ring of three unbaited traps was placed at 2 m and a second at 5 m from the central baited trap. Statistically robust results demonstrated clearly that the configuration of one central baited trap plus three unbaited satellite traps collected twice as many beetles on average over the season compared to the baited control trap. Addition of a second ring of unbaited traps increased collections by only about 20%, but this experiment indicated that trap catches dropped off exponentially with distance from the centre. The number of beetles caught in the baited traps was essentially the same in all 3 arrangements, suggesting that the additional unbaited traps captured beetles that otherwise may not have been captured.