Mitochondrial Genetic Diversity in the Bird Cherry-Oat Aphid Rhopalosiphum padi (L.) in China

Mitochondrial DNA (mtDNA) is an important genetic marker in population and evolutionary biology. To test the feasibility of two mitochondrial gene markers (COI and Cytb) for Rhopalosiphum padi, we collected 275 individuals of the insect species from 15 locations, which cover most of the species’ distribution range in China, and analyzed the diversity of the two genes. Seven COI haplotypes and 15 Cytb haplotypes were identified by 13 and 36 polymorphic sites, respectively. Across the entire samples, the average haplotype diversities (Hd) of COI and Cytb were 0.491 and 0.607, and the nucleotide diversities (π) of COI and Cytb were 0.147% and 0.160%, respectively. Relatively low levels of genetic diversity and genetic differentiation were observed among all R. padi populations based on the two genes. Moreover, parsimony networks of the COI and Cytb haplotypes of R. padi all supported a single clade. Although the nucleotide variation of mitochondrial genes has been used in other insect species, reviewing the recent literatures on mitochondrial diversity in aphid species, we found that the population and evolutionary biology of aphids including R. padi, could not be elucidated by analyzing mtDNA alone, mostly because of the low genetic variation of mitochondrial genetic markers among populations. We suggest the combined use of mtDNA and other genetic markers, such as microsatellites, to overcome the low genetic information provided by mtDNA in evolutionary studies on aphid populations.