Molecular mechanisms of olfactory detection in Spodoptera littoralis: Deorphanization of odorant receptors via the Drosophila empty neuron system

The olfactory sense determines vital steps in insect behaviour, including mate and food search, oviposition site selection and predator/parasitoid avoidance. As part of an international collaboration, we have established the noctuid moth, Spodoptera littoralis (the Egyptian Cotton Leafworm) as a model for investigation of noctuid olfaction and chemical ecology. At the molecular level, the fundamental units mediating insect interactions with the olfactory environment are odorant receptor (OR) proteins, which are functionally expressed in odorant receptor neurons within olfactory appendages, primarily the antennae.

One primary research focus has been functional characterization of the S. littoralis OR genes, which we recently identified in this species. We are seeking to determine the receptive range of each OR via deorphanisation experiments in a heterologous expression system. Individual ORs are currently being expressed in the Empty Neuron system of the vinegar fly, Drosophila melanogaster, to characterize their response profiles by means of single sensillum electrophysiological recordings (SSR). We have also utilized gas chromatographic analysis of plant headspace extracts, coupled to single sensillum recordings (GC-SSR) to analyze the tuning of specific ORs to components of ecologically relevant complex odor blends. Preliminary data demonstrate successful adaptation of these methods to the deorphanisation of S. littoralis ORs. These results represent an important step in understanding the molecular mechanisms of olfactory mediated behaviours in S. littoralis.