Abstract
Over 95% of feeding balsam woolly aphids occur in crevices on balsam fir branches and the highest density occurs within the 3-year tip of branches. The crevices occur under the bud scales at nodes, the base of each season’s growth, and among staminate flower buds or among and within flower bracts. The abundance and survival of aphids as well as mortality factors vary with the location of the nodes in a branch, the type of branch, and aphid generation. The significant differences show that there are 9 to 13 strata within the 3-year tip of a branch. For ecological studies and measuring population levels, the cluster of aphids within a defined crevice, for example under the bud scale at the base of a cluster of shoots, can be selected as a sample unit.