Examination of the status of Protaphis (Hemiptera: Aphididae)

Abstract: Protaphis used to be classified as a subgenus of Aphis. It was recently elevated to genus based on morphological characters. However, the newly subgenus Pseudoprotaphis of Aphis contains morphological characters, which overlap with those that belong to Protaphis. Currently, the North American species: A. caliginosa, A. debilicornis, A. lugentis and A. echinaceae are classified within the subgenus Aphis, but they are morphologically similar to the North American species A. knowltoni and A. middletonii, that are classified within Protaphis. Members of this group share peculiar morphological characters such as siphunculi as short as cauda, large marginal abdominal tubercles, secondary sensoria on antennal segments III, IV and V of most apterous morphs, and feeding primarily on roots and leaves of Asteraceae. Should Protaphis and Pseudoprotaphis be synonymized? Should these groups remain as subgenera of Aphis? What do these characters tell us about the evolution of these species? In order to answer these questions we reconstructed the phylogeny of the genus Aphis using morphological characters, mitochondrial COI and nuclear EF-1α genes. Our results show that A. debilicornis, A. echinaceae, A. middletonii and A. (Protaphis) terricola form a monophyletic clade indicating that they have the same common ancestor, and should belong to the same rank. However, we still need more evidences to determine if Protaphis and Pseudoprotaphis are valid.