Abstract: Small subunit nuclear ribosomal DNA (SSU rDNA or 18S rDNA) sequences were used to examine the phylogenetic relationships of families of Acridoidea. The SSU rDNA complete sequences (average length 1 844 bp) of the Acridoidea (include 8 families) were determined, and the homologous sequences of 8 relative species (including 6 species of Acridoidea and 2 species of Tetrigoidea) were retrieved from GenBank. The molecular phylogenetic trees were constructed with software package Clustal X (1.81), MEGA and PHYLIP using Tetrigoidea as outgroup. Based the phylogenetic trees thus obtained, we made the following conclusions: (1) The Acridoide a was supported as a monophyletic group; (2) Pyrgomorphidae and Chrotogonidae were the most ancestral groups; (3) Gomphoceridae and Arcypteridae have closer phylogenetic relationships; (4) Oedipodidae was the most evolved group; (5) The relative frequencies of the four nucleotides were approximately equal (A∶C∶G∶ T = 0.240∶0.239∶0.279∶0.242), SSU rDNA sequences were conserved and the transition ratio was higher than or approaching to the transversion ratio; (6) Different superfamilies and families were separated, the members of the same family were mostly grouped together, thus, the SSU rDNA sequences can be used as candidate nucleotide sequence for studying the phylogenetic relationships of Acridoidea .

Key words: Acridoidea, SSU rDNA, molecular phylogeny