Morphometric variation between populations of the balsam woolly aphid, Adelges piceae (Ratzeburg) (Homoptera: Adelgidae), in North America

Abstract

Morphological variation in characters of the first-instar and the adult stage of the balsam woolly aphid, Adelges piceae (Ratzeburg) (Homoptera: Adelgidae), were studied. Multiple discriminant analysis and UPGMA cluster analysis of the Mahalanobis generalized distances were used to classify 18 population samples collected on five Abies species throughout the known area of distribution. The populations were separated into three distinct groups: a "Maritime" group, a "British Columbia" group, and an "intermediate" group which consisted of samples from North Carolina, Oregon, and Washington. Variables taken from the adult morph gave a more consistent and, hence, a more reliable classification than the first-instar variables. Allocation of individual specimens into the three groups, as determined by identification functions, showed that the morphological characters measured in the adult stage correctly identified 85% of the specimens.It is suggested that the observed morphological divergence between eastern and western populations of A. piceae reflects the aphid's colonization history in North America. The importance of these findings for control is noted.