Molecular and morphological differentiation between Aphis gossypii Glover (Hemiptera, Aphididae) and related species, with particular reference to the North American Midwest

The cotton aphid, Aphis gossypii, is one of the most biologically diverse species of aphids; a polyphagous species in a family where most are host specialists. It is economically important and belongs to a group of closely related species that has challenged aphid taxonomy. The research presented here seeks to clarify the taxonomic relationships and status of species within the A. gossypii group in the North American Midwest. Sequences of the mitochondrial cytochrome oxidase 1 (COI), nuclear elongation factor 1-α (EF1-α), and nuclear sodium channel para-type (SCP) genes were used to differentiate between A. gossypii and related species. Aphis monardae, previously synonymised with A. gossypii, is re-established as a valid species. Phylogenetic analyses support the close relationship of members of the A. gossypii group native to North America (A. forbesi, A. monardae, A. oestlundi, A. rubifolii, and A. rubicola), Europe (A. nasturtii, A. urticata and A. sedi), and Asia (A. agrimoniae, A. clerodendri, A. glycines, A. gossypii, A. hypericiphaga, A. ichigicola, A. ichigo, A. sanguisorbicola, A. sumire and A. taraxicicola). The North American species most closely related to A. gossypii are A. monardae and A. oestlundi. The cosmopolitan A. gossypii and A. sedi identified in the USA are genetically very similar using COI and EF1-α sequences, but the SCP gene shows greater genetic distance between them. We present a discussion of the biological and morphological differentiation of these species.