DO BALSAM TWIG APHIDS (HOMOPTERA: APHIDIDAE) LOWER TREE SUSCEPTIBILITY TO SPRUCE BUDWORM?

Can. Ent. 121: 93-103 (1989) The balsam twig aphid, Mindarus abietinus Koch, infested nearly all trees in a rangewide provenance plantation of balsam fir, Abies balsamea (L.) Mill., in Michigan. Infestation levels were highest on eastern and lowest on western seed sources of fir. Large populations of the aphid were correlated with low survival and reduced developmental rates of the spruce budworm, Choristoneurafurniferana (Clemens). We propose that chronic, high susceptibility of trees to aphids could reduce concomitant susceptibility to budworm through direct (competition) and indirect (host and communitylevel) effects.