Comparison of the efficacy of pheromone-baited traps, pheromone-baited trees, and felled trees for the control of Dendroctonus pseudotsugae (Coleoptera: Scolytidae)

Abstract

Alternative methods for controlling Douglas-fir beetles, Dendroctonus pseudotsugae Hopkins (Coleoptera: Scolytidae), were examined in terms of the number of beetles removed from a population and in terms of beetle flight activity near treated sites. Methods that were tested included pheromone-baited Lindgren funnel traps, standing, continuously pheromone-baited trees, standing, temporarily pheromone-baited trees with bait removed after beetles began invading the tree, and single felled trees. Funnel traps captured more than twice the number of beetles over the flight season than a baited or felled trees. The tree methods did not differ from each other in the number of beetles captured. Trees in all three methods became saturated within the first 20-30 d of flight. Baited traps continued to catch beetles during the whole test period. Beetle flight remained active around continuously baited trees even after beetle attacks ceased. Beetle flight around temporarily baited trees ceased after the trees became saturated. Density of beetles per tree did not differ between different sized decks of felled trees. Large decks (with 9 to 12 trees) absorbed three times the beetles than small decks (with 3 to 4 trees), and nine times as many as did single felled trees. Spillover to neighboring trees from baited trees or traps is minimized when baits are removed after initial attacks. A tree deck of three or four felled trees of DBH ≈40 em is equivalent to one trap in terms of the number of beetles removed. Trees in a deck become saturated within the same time span as trees in the other methods. Single felled trees or decks produce no spillover into the neighboring stand.