Oviposition deterring components in larval frass of Spodoptera littoralis (Boisd) (Lepidoptera, Noctuidae): a behavioral and electrophysiological evaluation

Oviposition in Spodoptera littoralis was strongly deterred by a mixture of six compounds, benzaldehyde and the five terpenes carvacrol, eugenol, nerolidol, phytol and thymol, identified from conspecific larval frass. If one of the compounds was excluded from the mixture the deterrent effect was lost. An electroantennogram-screening was performed on 15 compounds identified from the larval frass. Of the behaviourally active compounds, dose-response relationships were obtained for benzaldehyde, eugenol and nerolidol. Seven types of receptor cells specifically tuned to compounds from the larval frass were identified by single-sensillum recordings from olfactory sensilla on the female antenna. The most abundant of these was a receptor cell type responding equally well to the three aromatic terpenes carvacrol, eugenol and thymol. Receptor cells responding to only a single terpene were found for carvacrol, eugenol, nerolidol and phytol. Receptor cells responding to other frass compounds, green leaf odours and sex pheromone components were also found. No receptor cell responding to benzaldehyde was identified