POLYMORPHISM OF THE HEREDITARY SIGMA VIRUS IN NATURAL POPULATIONS OF DROSOPHILA MELANOGASTER

Previous studies have shown that, in natural French populations of Drosophila melanogaster, 10 to 20% of the flies are infected by the noncontagious, hereditary rhabdovirus sigma responsible for CO2 sensitivity. These populations are also polymorphic for two alleles [ref(2)Po and ref(2)Pp of a gene for resistance to the sigma virus. Evidence is given here that two viral genetic types, differing in their response to the ref(2)Pp allele, are present in these populations of flies; the most common type is only slightly sensitive to the ref(2)Pp allele.