The same functional types of plant odorant receptor neurones in male and female heliothine moths

The specificity of the pheromone receptor neurone types are well described in heliothine males (e.g. Berg et al. 1998, 1995), whereas neurones detecting plant odorants have only been studied in the females. Nineteen plant odorant receptor neurone types have been functionally characterised in female heliothine moths using gas chromatography linked to single cell recordings and to mass spectrometry (Røstelien et al. 2005, Stranden et al. 2003). The presence of the same number of ordinary glomeruli in both sexes (Skiri et al. 2005, Berg et al. 2002) indicates that they have the same number of plant odorant receptor neurone types. To identify as many odorants as possible, blends of volatiles produced by hosts and non-host plants as well as chemical standards were used as test samples. The protocols used for screening volatiles on female receptor neurones were also used for studying the males. In addition, insect produced volatiles and new plant volatiles were included in the test protocol. Screening the neurones with the GC-separated volatiles of the complex blends excluded a large number of molecules as odorants. All neurones responded strongest to one compound (primary odorant) and weaker to a few structurally related compounds (secondary odorants). The neurone types were named according to the primary odorant. Eight plant odorant receptor neurone types have so far been identified in the Heliothis virescens males. They are similar to the types identified in females. One example is the (-)-germacrene D neurones. They have identical molecular receptive ranges with the female neurons and seem to be the most common neurone type also in the males. Including new plant samples in the protocol also gave new information about the molecular receptive range of some of the neurone types. For instance, the neurone type identified as tuned to 2-phenyl ethanol in the females was also recorded from males, but being even more sensitive to phenyl acetaldehyde. The new information concerning the pheromone receptor neurones was inhibition elicited by one or a few plant odorants. Although more information in males is needed, the overall results suggest that males and females possess the same type of plant odorant receptor neurones.