SEMIOCHEMICAL-INDUCED COMPETITION BETWEEN DENDROCTONUS-RUFIPENNIS AND2 SECONDARY SPECIES, IPS-TRIDENS AND DRYOCOETES-AFFABER (COLEOPTERA, SCOLYTIDAE)

We investigated the hypothesis that interspecific interactions between the spruce beetle, Dendroctonus rufipennis Kirby, and 2 secondary spe cies, Ips tridens Mannerheim and Dryocoetes affaber Mannerheim, advers ely affect spruce beetle progeny production and survival. In field exp eriments in the British Columbia interior, attack by the secondary spe cies was induced by placing pheromone baits on felled trees just after spruce beetle attack. Spruce beetle attack densities, gallery length per square meter, and progeny densities Mere significantly reduced in trees that were baited. with D. affaber pheromones or D. affaber and I tridens pheromones. Resource exploitation and synomonal interference with subsequent spruce beetle attacks were the primary competitive mec hanisms. No evidence for direct interference was found. Because the im pact of the secondary species was not pronounced, semiochemical-induce d competitive displacement of the spruce beetle after it has establish ed would not be practical for retarding the development of, or suppres sing, beetle outbreaks.