MITOCHONDRIAL-DNA VARIATION IN RHOPALOSIPHUM-PADI (HOMOPTERA, APHIDIDAE) POPULATIONS FROM 4 SPANISH LOCALITIES

In total, 35 clones of the bird cherry-oat aphid, Rhopalosiphum padi (L.) established from samples collected in four distant localities of Spain during fall 1989 and spring 1990 were examined for mitochondrial DNA variation using 20 restriction endonucleases. Individual parthenogenetic adults were used to establish clonal lines on wheat ('Talento') seedlings. Restriction site polymorphism was detected only with endonuclease RsaI, but no statistical treatment of data could be done until more polymorphic endonucleases are found. Length variation of the mitochondrial DNA molecule, however, was extensive among R. padi clones. Distribution among populations of this size polymorphism was used to estimate total and within-population diversity indexes. The population structure index was estimated to be 0.28. This value was compared with the corresponding diversity index obtained by allozyme analysis for the less migratory (more structured) aphid Macrosiphum rosae (L.). Our results show that the mitochondrial DNA methodology is a very promising tool for analyzing aphid population structure and for studying its relationships with the epidemiology of aphid-transmitted disease agents such as barley yellow dwarf virus.