Numbers of Dendroctonus rufipennis (Kirby) and Thanasimus undatulus Say at pheromone-baited poisoned and unpoisoned trees

Four times as many spruce beetles, <i>Dendroctonus rufipennis<i> (Kirby), were killed at spruce trees (<i>Picea engelmannii</i> Parry and <i>Picea glauca</i> (Moench) Voss) baited with frontalin and sprayed with insecticide than at trees baited but unsprayed. Many clerid predators, <i>Thanasimus undulatus</i> Say, were also killed at the baited and sprayed trees. Their numbers were correlated with those of killed spruce beetles. Other correlations show that sprayed and unsprayed trees were exposed to the same attacking spruce beetle population and that predation on the spruce beetles was occurring