Sequencing and characterization of six cDNAs putatively encoding three pairs of pheromone receptors in two sibling species, Helicoverpa armigera and Helicoverpa assulta.

Pheromone receptors (PRs) on male antennae mediate specific and sensitive detection of sex pheromone components in lepidopterans. In this study, we identified and sequenced six putative cDNAs encoding PRs from sibling species, namely HarmOR1, HarmOR2 and HarmOR3 in Helicoverpa armigera and HassOR1, HassOR2 and HassOR3 in Helicoverpa assulta, which appeared to be orthologs of Heliothis virescens putative PR genes HvOR13, HvOR11 and HvOR16, respectively. Expression patterns of the six PR genes were evaluated by quantitative real-time PCR (qRT-PCR). All the putative PR genes exhibited male-biased expression patterns in adult antennae except for HarmOR2 and HassOR2 that showed similar expression levels in male and female antennae. Expression level of HarmOR1 was significantly higher than those of HarmOR2 and HarmOR3 in male antennae of H. armigera, but the three corresponding PR genes in male antennae of H. assulta showed similar expression levels. This implies the role of the PR encoded by HarmOR1 for interacting with Z11-16:Ald. The level of HarmOR1 transcript was significantly higher than that of HassOR1. These results were consistent with the ratio of Z11-16:Ald in their sex pheromone blends and the abundance of sensilla tuned to Z11-16:Ald on antennae of male adults of the two species.