Reassessment of the phylogeography and intraspecific relationships of western and eastern populations of the boll weevil, Anthonomus grandis Boheman (Coleoptera: Curculionidae), in North America

Nucleotide sequences from a segment of the mitochondrial cytochrome c oxidase subunit I (COI) gene were used to examine phylogeography, intraspecific relationships and taxonomy of the boll weevil Anthonomus grandis Boheman (Coleoptera: Curculionidae) collected from wild and cultivated cotton hosts in Mexico and USA. Phylogenetic trees and TCS haplotype networks showed that boll weevils partitioned into two clusters: 'western' and 'eastern'. In addition to infesting cultivated cotton, Gossypium hirsutum, both groups were found on several other species of the cotton tribe Gossypieae: wild Gossypium, Hampea, Cienfuegosia and Hibiscus pernambucensis (eastern group only). No evidence was found for host plant-associated genetic differentiation in either group. The level of genetic divergence and lack of shared COI haplotypes, combined with five apparent fixed nucleotide differences between the two groups and earlier evidence of reproductive isolation, together provide strong support for reinstating the subspecies name, Anthonomus grandis thurberiae Pierce, for the western lineage. Demographic tests suggested that both lineages have undergone population expansions dating to the Pleistocene. A possible vicariant role for the Trans-Mexican Volcanic Belt and the Sierra Madre Occidental in promoting genetic divergence, and a reassessment of dispersal scenarios during the postulated northward expansion of A. g. thurberiae are discussed.