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 at a worldwide scale. Recent population genetic studies have traced their invasion routes and demonstrated that bottlenecks in population size have reduced their genetic diversity. As a consequence, phenotypical differences were highlighted between native and invasive populations. Among phenotypical traits, cuticular hydrocarbons (CHCs) might reflect geographical origin of a lady beetle, especially because of their genetic basis. Here, we investigated 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 were solvent-extracted before being quantified and identified by gas chromatography and mass spectrometry. We detected a total of 17 CHCs from female elytra including six alkanes, three polyunsaturated and eight monounsaturated alkenes. The total quantity of CHCs differed among the populations with lady beetles from Tai’an (China) displaying a higher CHCs concentration than lady beetles from Gembloux (Belgium) and from Beijing (China) populations. Multivariate analyses detected differences in CHCs qualitative profiles, with females from Tai’an being different from the two other populations. Finally, our behavioural assays showed that females originating from the native Tai’an population were less preferred by males, while females from the invasive population were mounted more often. Our behavioural assays suggest that CHCs are not involved in discrimination of mating partners based on their origin.