Genetic Divergence among Populations of the White Pine Weevil, Pissodes strobi (Coleoptera: Curculionidae)

Abstract

Genetic differences among 17 transcontinentally distributed populations of the white pine weevil, Pissodes strobi (Peck), were assessed by examining electrophoretic variation at 11 enzyme loci. Genetic identity values for all paired comparisons ranged from 0.899-0.998 (mean = 0.963) and no fixed-allele differences were detected among populations at any locus. F statistics for different interpopulational comparisons were 0.025 (regions compared with total), 0.098 (populations compared with total), and 0.075 (populations compared with regions). Significant heterogeneity in allele frequencies at polymorphic loci was observed among populations. Phenetic cluster analysis based on genetic identity or distance values failed to group populations according to geographic region, and regression analysis revealed that the genetic identity between populations was not closely dependent on the geographic distance between them. Overall genetic variation, measured by the percentage of polymorphic loci and mean heterozygosity, was lower in western populations than in those from the East. This pattern of variation may have resulted from a series of founder events as P. strobi presumably expanded its range from east to west, or it may reflect a positive correlation with environmental heterogeneity, as suggested by the narrowing of host range (generalist to specialist) from east to west.