RFLP analysis was developed and tested on three biotypes of the aphid Amphorophora idaei and one population of A. rubi. Using a 32P end-labelled 15 bp oligonucleotide from M13 protein III gene and a 32P randomly primed flax ribosomal DNA probe, RFLP analysis clearly differentiated the two closely related species and the three A. idaei biotypes tested. RFLP patterns for A. idaei clones were stable over 50 parthenogenetic generations.