MOLECULAR PHYLOGENY OF THE HOMOPTERA - A PARAPHYLETIC TAXON

Homoptera and Heteroptera comprise a large insect assemblage, the Hemi ptera. Many of the plant sap-sucking Homoptera possess unusual and com plex life histories and depend on maternally inherited, intracellular bacteria to supplement their nutritionally deficient diets. Presumably in connection with their diet and lifestyles, the morphology of many Homoptera has become greatly reduced, leading to major controversies r egarding the phylogenetic affiliations of homopteran superfamilies. Th e most fundamental question concerns whether the Homoptera as a whole are monophyletic. Recent studies based on morphology have argued that the Homoptera Sternorrhyncha (Aphidoidea, Coccoidea, Psylloidea, Aleyr odoidea) is a sister group to a group comprising the Homoptera Aucheno rrhyncha (Fulgoroidea, Cicadoidea, Cercopoidea, Cicadelloidea) and the Heteroptera, making the Homoptera paraphyletic. We sequenced the 5' 5 80-680 base pairs of small-subunit (18S) ribosomal DNA from a selectio n of Homoptera, Hemiptera, and their putative outgroups, the Thysanopt era and Psocoptera, to apply molecular characters to the problem of Ho moptera phylogeny. Parsimony, distance, maximum-likelihood, and bootst rap methods were used to construct trees from sequence data and assess support for the topologies produced. Molecular data corroborate curre nt views of relationships within the Sternorrhyncha and Auchenorrhynch a based on morphology and strongly support the hypothesis of homoptera n paraphyly as stated above. In addition, it was found that Homoptera Sternorrhyncha have extra, GC-rich sequence concentrated in a variable region of the 18S rDNA, which indicates that some unique evolutionary processes are occurring in this lineage.