Systematics and ecology of the Anthonomus grandis species complex (Coleoptera: Curculionidae) and their Hampea host plants (Malvales: Malvaceae)

The systematics of species of the Anthonomus grandis species complex and their Hampea host plants were analyzed using morphometric and phylogenetic analyses of morphological characters. Of eight species of Hampea examined in the field in Mexico and Central America, four were found to support populations of weevils of the A. grandis complex. Based on morphometric analysis and comparison of distinct character states of these weevils with A. grandis and A. hunteri, it was concluded that three undescribed species are represented. These species are compared, described and illustrated herein. Phylogenetic analysis of the A. grandis species complex indicated that it consists of two major clades. In the first clade, A. grandis is the sister taxon of A. hunteri and an undescribed species from Hampea appendiculata Standley. The second clade contains two undescribed species, one of which occurs on Hampea mexicana Fryxell and the second on both Hampea longipes Miranda and Hampea montebellensis Fryxell. The proposed weevil phylogeny strongly supports the hypothesis that Hampea is the original host plant genus of the A. grandis complex. Phylogenetic analysis of Hampea suggests that the genus speciated in southern Mexico and Guatemala and later dispersed southward and northward. Comparison of the phylogeny of the A. grandis complex with that of Hampea showed little congruence, suggesting weevil species are associated with Hampea as a result of host shifts and colonization processes as opposed to cospeciation (parallel cladogenesis). Mapping habitat associations and geographic distributions onto the phylogeny of the A. grandis complex indicate that weevil preference for general habitat type (montane vs. lowland habitats) and geographic proximity of Hampea were probably the principal factors responsible for observed associations of Anthonomus weevils with Hampea. Other possible factors of importance in speciation of the A. grandis species complex including plant phenology, bud size, bud morphology and overall reproductive output, were evaluated from field studies of three species of Hampea and their associated Anthonomus weevils. The possible factors responsible for A. grandis becoming a serious pest of cultivated cotton are also discussed in light of the systematic and ecological findings.