GEOGRAPHIC-DISTRIBUTION AND SEASONAL-VARIATION OF MITOCHONDRIAL-DNA HAPLOTYPES IN THE APHID RHOPALOSIPHUM-PADI (HEMIPTERA, APHIDIDAE)

This study examines the spatial and seasonal patterning of mitochondri al DNA diversity in French populations of the bird cherry-oat aphid, R hopalosiphum padi (Linnaeus), on both its primary and secondary hosts. Our results confirm the presence of two major mitochondrial lineages that are generally associated with the breeding system variation (cycl ic and obligate parthenogenesis) shown by this species. The strength o f this relationship varies regionally, being most evident in the south and west. Cyclically parthenogenetic populations show no significant regional or seasonal genetic divergence reflecting high levels of gene flow, possibly promoted by their obligate host-alternation. However, obligately parthenogenetic populations show a north-south dine in the distribution of the dominant haplotypes. This pattern might result fro m a selective advantage of some obligately parthenogenetic lineages un der cold temperature regime. Alternatively, this dine might be establi shed by a gradient in the intensity of nuclear gene flow between cycli cally and obligately parthenogenetic populations mediated by androcycl ic males. The discrimination between these possible explanations will require extending analysis to include hypervariable nuclear markers.