Life-cycle profiling of cuticular hydrocarbons in the cotton bollworm Helicoverpa armigera (Lepidoptera: Noctuidae)

Cuticular hydrocarbons (CHCs) are the main components of the wax layer present on insects’ surface, serving as protective agents against environmental stress and/or as communication signals. It has been documented that the chemical composition of CHCs varies with species and even with developmental stage or sex of the same species. However, studies involving in a life-cycle identification of CHCs are rare. In this work, we attempted to profile the components and relative abundance of CHCs in the cotton bollworm Helicoverpa armigera at all the four developmental stages and in both sexes of pupae and adults. A total of 29 CHCs were putatively identified by gas chromatography-mass spectrometer analysis, including 14 n-alkanes, 4 methyl-branched alkenes and 11 methyl-branched alkanes, with 15 of them being detected at all the four developmental stages. Of the 29 CHCs, the straight-chain alkanes with 27, 29 and 31 carbon atoms were the major CHCs. All three classes of CHCs (n-alkanes, methyl-branched alkanes and methyl-branched alkenes) were found in both larvae and pupae, while no unsaturated hydrocarbons were observed in eggs and adults. Methyl-branched alkanes were the main component found in eggs and adults, while the composition of n-alkanes and methyl-branched alkanes in larvae and pupae varied with ages. Principal component analysis (PCA) revealed that the CHC profiles in larvae and adults changed significantly with ages, while the CHC profiles in early pupae (1-day-old) showed distinct difference from those of late pupae. Furthermore, sexual dimorphism in the CHC profile was observed in mature adults (3-day-old and 5-day-old), with male adults possessing more n-C31 and n-C33, but less 3-MeC29 than females.