Seasonal cycles of reproductive behavior in native populations of Harmonia axyridis around Beijing, China

Melanic forms of H. axyridis are rare in invasive populations, but are commonly observed in the species' native range in China, Korea and Japan. Annually, there are two distinct generations of H. axyridis around Beijing, China. In autumn, melanic forms are outnumbered by succinic (non-melanic) forms by 5:1, but the two forms are equally abundant in spring. These seasonal changes in phenotype frequencies are driven by seasonal shifts in mate preference in the preceding generation and can be explained by the thermal advantages of melanism in the winter generation and its disadantages in the summer generation. We examined the nature of assortative mating in H. axyridis using choice and no choice mating tests and found that pair formation was largely under female control, but males controlled duration of copula. Female H. axyridis expressed mate preference overtly, by rejecting less-preferred phenotypes, and cryptically, by retaining their eggs for longer periods after matings with less-preferred males, ostensibly to replace their sperm. The strength of a female's preference for a particular male phenotype was dependent on her own phenotype, and other gender-specific reproductive behaviors varied markedly between winter and summer generations, in some cases independent of phenotype. Some phenomena were consistent with pleiotropic effects of melanic alleles, whereas others were suggestive of maternally-mediated epigenetic factors.