Molecular Phylogeny and Species Recognition in the Mealybug Genus Ferrisia Fullaway (Hemiptera: Pseudococcidae)

Abstract

Previous allozyme and DNA nucleotide sequence studies of the mealybug genus Ferrisia Fullaway (Hemiptera: Pseudococcidae), although limited, have suggested greater species diversity than is recognized by the current morphology-based taxonomy. Here we analyse nucleotide sequence data from one mitochondrial (cytochrome oxidase I) and two nuclear (EF-1 alpha and 28S D2D3) genes and recover ten well-supported groups that allow us to reassess the taxonomic utility of morphological characters used for species recognition. We report on previously used morphological characters for which states are highly variable within genetic groups and identify new characters (of the wax-exuding cuticular ducts and pores) with taxonomically informative states. The widespread pest species F. virgata (Cockerell), commonly called the striped mealybug, should be diagnosed more narrowly. From samples identified as F. virgata, we recover six clades that we equate with species and that can be distinguished with the newly identified morphological characters. We determine that five of the 'electrophoretic species' identified informally by the late Uzi Nur based on electrophoretic mobility of 20 enzymes correlate with four of our genetic groups. This matching of Nur's putative species with ours was possible only because some of Nur's slide-mounted voucher specimens were deposited in a museum and thus available for morphological study. Species confused with F. virgata are either new to science or were placed erroneously in synonymy with F. virgata by earlier authors: they will be described elsewhere. The most important characters of the adult female for distinguishing these species from F. virgata are the positions and characteristics of minute discoidal pore(s) associated both with the ventral oral-collar tubular ducts and with the sclerotized area surrounding each dorsal enlarged tubular duct, and the number of sizes of the ventral oral-collar tubular ducts. In addition, we determine that adult females of F. gilli Gullan from different populations on different host plants vary substantially in the number and size of clusters of small ventral oral-collar ducts on the body margins - features previously suspected to indicate distinct species.