Low genetic diversity among pea aphid (Acyrthosiphon pisum) biotypes of different plant affiliation

Genetic diversity in the pea aphid Acyrthosiphon pisum was investigated by a restriction fragment length polymorphism (RFLP) analysis of three materna lly inherited genomes (mitochondrial DNA and plasmids of the symbiotic bact eria Buchnera). Twenty-nine parthenogenetic clones of three A. pisum biotyp es, defined by their capacity to use the legume crops pea, alfalfa and red clover, respectively, were analysed, and a total of 67 restriction sites wa s scored. No restriction site variation in the mitochondrial genome was obt ained, but length variation at two regions (the A + T-rich region and ND3-N D5 region) was noted. One aphid clone bore a variant HindIII restriction si te in the Buchnera leucine plasmid (pAPEleu), and two clones were heteropla smic for a 0.76-kb deletion in the Buchner a tryptophan plasmid (pAPEtrp). Based on arthropod nucleotide substitution rates, it is proposed that the c rop-feeding biotypes of A. pisum may have diversified within the last 100 0 00 years and possibly much more recently, since the advent of agriculture.