Systematics of brown planthopper and related species using nuclear and mitochondrial DNA

The brown planthopper, NiIaparvata lugens, is a serious pest of rice in tropical and temperate Asia, and northern Australia. This study aimed to derive a phylogeny of N. lugens and other species in the genus, and to obtain molecular markers for the different species. Four populations of N. lugens collected from rice, and three populations of a morphologically indistinguishable species, collected from a wild grass, Leersia, were analysed. Single populations of N. bakeri, a sibling species of N. lugens, N. muiri and a West African species, N. maeander, were also included in the study. Molecular phylogenies were inferred following amplification and restriction site analysis of part of the 16S RNA gene and a region between the cytochrome oxidase subunits I and II of the mitochondrial DNA. The mitochondrial DNA showed limited variability between populations but the data implied that N. bakeri and N. maeander are closely related, as are N. muiri and N. lugens. Amplification and restriction site analysis of 57 sites in the nuclear 18S rRNA gene revealed one variable site in the DNA from N. maeander. DNA sequences of one of the nuclear ribosomal DNA internal transcribed spacers were used to infer a phylogeny which agreed with the predicted species relationships. The nuclear DNA phylogeny strongly supported a division between the N. lugens populations in Asia and Australia, regardless of host plant associations. A partial genomic library was constructed from total N. lugens DNA, and nine low-copy DNA clones selected and partially sequenced. Seven of these loci were amplified from N. lugens DNA and four from N. bakeri DNA. Restriction site analysis of the loci revealed restriction sites characteristic for N. lugens populations from the alternative host plants. A phylogeny inferred from the data supported a division between the N. lugens populations from Asia and Australia. The combined analysis of all the molecular data supported the inference that the Asian and Australian N. lugens populations are separate species.