Intraspecific nucleotide variation at the pheromone binding protein locus in the turnip moth, Agrotis segetum

Inter- and intraspecific amino acid variability in the pheromone binding pr oteins (PBPs) of the Lepidoptera is believed to contribute to a molecular m echanism of pheromone blend discrimination. Messenger RNA coding for PBP se quence in Agrotis segetum (Noctuidae) was cloned, and nucleotide and inferr ed amino acid variation across a 769-bp region of a PBP locus was studied i n two populations. A single gene copy was fully sequenced, revealing an int ron/exon structure conserved with distant saturniids. While several nucleot ide substitutions are predicted to result in amino acid replacement, tests for the presence of natural selection suggest that the observed variation i s neutral. A phylogenetic analysis provides evidence that the two populatio ns are in the process of genetic isolation.