REASSESSMENT OF DALBULUS LEAFHOPPER (HOMOPTERA, CICADELLIDAE) PHYLOGENY BASED ON MITOCHONDRIAL-DNA SEQUENCES

Conflicting hypotheses of phylogenetic relationships among leafhopper species in the genus Dalbulus deLong have resulted from analyses of mo rphological and allozyme data. To improve the phylogenetic estimate, n ucleotide sequence data from 340 bp of the mitochondrial 12S rDNA gene and 942 bp of the NADH dehydrogenase 1 (ND1) gene were compiled for 1 0 species of Dalbulus, 1 species of its putative sister group, Baldulu s, and 2 outgroups. Intraspecific branch lengths were estimated for Da lbulus gelbus DeLong, Dalbulus maidis (DeLong and Wolcott), and Baldul us tripsaci Kramer and Whitcomb. Sequences were aligned based on secon dary structure models of the 12S gene and along codons in the ND1 gene . Phylogenetic analyses of the sequence data using maximum parsimony, genetic distance-neighbor joining and maximum likelihood methods yield ed nearly identical results. A test for incongruence indicated that th e phylogenetic estimate based on sequence data was not significantly d ifferent from that derived based on morphological characters. Allozyme data yielded a topology that was significantly incongruent with both morphological and sequence data. Therefore, the morphological and sequ ence datasets were combined into a single analysis, which yielded a we ll-resolved phylogenetic estimate for Dalbulus. The resulting tree sup ports the hypothesis that the ancestral hosts of Dalbulus were gamagra sses (Tripsacum spp.) and that the acquisition of a preference for mai ze (Zea mays) arose independently in 2 Dalbulus lineages.