The taste of origin in a lady beetle: do males discriminate between females based on cuticular hydrocarbons?
The Asian lady beetle Harmonia axyridis originates from Asia and has established invasive populations worldwide. Recent population genetic studies trace their invasion routes and demonstrate that bottlenecks in population size have reduced their genetic diversity. Consequently, phenotypical differences are highlighted between native and invasive populations. Among phenotypical traits, cuticular hydrocarbons (CHCs) might reflect the geographical origin of a lady beetle, especially because of their genetic basis. The present study investigates whether (i) the CHC profiles qualitatively and quantitatively differ between females of H. axyridis from native and invasive populations and (ii) males discriminate females from native and invasive populations using CHC profiles. CHCs are solvent-extracted before being quantified and identified by gas chromatography and mass spectrometry. In total, 17 CHCs are detected from female elytra, including six alkanes, three polyunsaturated and eight monounsaturated alkenes. The total quantity of CHCs differs among the populations, with lady beetles from Tai'an (China) displaying higher CHC concentrations than lady beetles from Gembloux (Belgium) and from Beijing (China) populations. Multivariate analyses detect differences in CHC qualitative profiles, with females from Tai'an being different from the two other populations. Finally, behavioural assays show that females originating from the native Tai'an population are less preferred by males, whereas females from the invasive population are mounted more often. The behavioural assays suggest that CHCs are not involved in discrimination of mating partners based on their origin.