Mitochondrial Dna Divergence among Greenbug (Homoptera: Aphididae) Biotypes

Relationships among greenbug, Schizaphis graminum (Rondani), biotypes B, C, E, and F were examined by comparison of mitochondrial DNA (mtDNA) restriction patterns. MtDNA was isolated from isofemale lineages, and the restriction fragments produced by 10 restriction endonucleases were end-labeled with 32P-nucleoside triphosphates by the large fragment of E. coli polymerase I. Restriction digests were electrophoretically separated on 20-cm agarose gels and visualized by autoradiography. Estimates of nucleotide sequence divergence were calculated. For biotype comparison B versus C and B versus E, the total proportion of shared fragments (F) was 0.73 and 0.77, respectively. Corresponding estimates of nucleotide sequence divergence were 1.2% and 1.0% estimates indicate a long period of time since these biotypes shared a common ancestral mitochondrial genome. The mitochondrial genomes of C and E shared a greater proportion of fragments (F = 0.96), with an estimated 0.17% sequence divergence. The mitochondrial data support previous conclusions about genetic divergence among biotypes B, C, and E drawn from chromosome-length measurements and multivariate analyses of alate males and females.