Molecular characterization of accessory proteins mediating sexual selection in two Ostrinia species

Sexual selection and mating in moths is mediated by olfactory sensing of pheromone blends. Differences between pheromone blends are detected at the periphery of the olfactory system by receptors and accessory proteins expressed in trichoid sensilla. Pheromone binding proteins (PBPs) and sensory neuron membrane proteins (SNMPs) are involved in pheromone detection, and may play a role in discrimination of pheromone blends. The European corn borer (Ostrinia nubilalis) (ECB) exists as two races, the Z-race uses (Z)-11-tetradecenyl acetate as the main component of its pheromone blend while the E-race uses (E)-11-tetradecenyl acetate. The related Asian corn borer (Ostrinia furnacalis) (ACB) uses a slightly different pheromone, (E) and (Z)-12-tetradecenyl acetate. We hypothesized that changes in the pheromone components are accompanied by changes in the sequence or expression level of the genes involved in their detection. Partial transcripts of 5 PBPs and 2 SNMPs were identified by pyrosequencing antennal cDNA. Complete cDNA sequences were obtained by rapid amplification of cDNA ends. Evidence of positive selection was analyzed by calculating the ratio of synonymous and non synonymous substitutions. Expression levels of PBPs and SNMPs in the antennae were measured using quantitative real-time PCR. There was no evidence for positive selection in the sequences or expression levels of the PBPs and SNMPs, and therefore these proteins are not likely to be involved in the discrimination of the ECB and ACB pheromones. This is the first report of multiple PBPs and SNMPs in ECB and ACB.