Morphological phylogeny of gall‐forming aphids of the tribe Eriosomatini (Aphididae: Eriosomatinae)

Abstract

Aphids of the tribe Eriosomatini are typically associated with the tree genera Ulmus and Zelkova as the primary host, on which they induce several types of leaf gall. To elucidate evolutionary changes in the aphid–host associations and gall morphology, phylogenetic relationships were inferred using 36 species (28 in the ingroup) and based on 52 morphological characters. Phylogenetic analysis with equal character weighting led to hundreds of most‐parsimonious trees, and the strict consensus of these was poorly resolved. However, the successive weighting of characters yielded three most‐parsimonious trees. The strict consensus of these supported the monophyly of the Eriosomatini and the monophyly of most genera. Reconstruction of the aphid–host associations on the consensus tree indicated that the ancestral Eriosomatini were associated with Zelkova and that the association with Ulmus evolved twice independently. Ancestral reconstruction suggests that galls of the leaf‐roll type are ancestral to those of the completely and incompletely closed pouch type, and that each type of pouch galls evolved independently. It is suggested that despite early diversification of the Eriosomatini on Zelkova species, Zelkova‐associated eriosomatines had become extinct or survived as relict parthenogens on the secondary host due to the elimination of Zelkova in most regions since the late Tertiary. In contrast, two large genera in the Eriosomatini, Eriosoma and Tetraneura, are associated with the largest elm section Ulmus whose elements are distributed widely in Eurasia, including boreal regions. Therefore, the available evidence suggests that the present species diversity and distribution patterns of the eriosomatines have been largely affected by the diversification and extinction of their host plants during the late Tertiary and Quaternary.