The effect of non-host plant volatiles on the reproductive behaviour of the Egyptian cotton leafworm, Spodoptera littoralis

Abstract: Spodoptera littoralis is a major pest of cotton in Egypt, causing serious economic losses. Egyptian farmers highly appreciate biological control of the pest as synthetic pesticides are very unsustainable. Phytophagous insects rely on plant volatiles to locate oviposition, feeding and, mating sites. We tested newly emerged S. littoralis moths by putting them in jars in indirect contact with leaves of the host plant, Gossypium hirsutum (Gh) and of non-host plants, Adhatoda vasica (Av) and Picea abies (Pa). Combinations of host and non-host plant leaves were also observed. Females kept with Gh leaves started calling earlier than the females in all non-host and the control treatments. Moths exhibited delayed mating when Pa and Gh leaves were offered in combination. Fecundity was reduced with strong to medium effect when Gh and Pa and, Gh and Av leaves were offered in combinations, respectively. Pair longevity was decreased in the absence of Gh leaves or the presence of Av and Pa leaves. Gas chromatogram electroantennographic detection (GC-EAD) study on the antennae of female S. littoralis moths revealed three bio-active peaks in headspace collections from Av and five in Pa, which were subsequently identified through gas chromatography mass spectrometry (GCMS) by a combination of MS library searches, Kovats indices calculating, and matching the retention times with synthetic standards if available. The biological activity of synthetic standards of the identified compounds was further confirmed through electro-antennogram dose-response tests (EAG). A comprehensive knowledge about these inhibitory effects of Av and Pa leaves or their combinations, or compounds derived from them, could lead to sustainable pest management policies.