Effects of the winter temperature regime on survival, body mass loss and post-winter starvation resistance in laboratory-reared and field-collected ladybirds.

Ongoing climate change results in increasing temperatures throughout the seasons. The effects of climate change on insect performance are less studied during the winter season than during the growing season. Here, we investigated the effects of various winter temperature regimes (warm, normal and cold) on the winter performance of the invasive ladybird Harmonia axyridis (Coleoptera: Coccinellidae). Winter survival, body mass loss and post-winter starvation resistance were measured for a laboratory-reared population as well as three populations collected from the field prior to overwintering. The warm winter regime increased the survival rate and body mass loss and reduced post-winter starvation resistance compared to those of the ladybirds in the cold winter regime. The effects of the temperature regime were qualitatively similar for the laboratory-reared and field-collected beetles; however, there were significant quantitative differences in all measured overwintering parameters between the laboratory-reared and field-collected populations. The winter survival of the laboratory-reared beetles was much lower than that of the field-collected beetles. The laboratory-reared beetles also lost a larger proportion of their body mass and had reduced post-winter starvation resistance. Winter survival was similar between the females and males, but compared to the males, the females lost a smaller proportion of their body mass and had better post-winter starvation resistance. The pre-overwintering body mass positively affected winter survival and post-winter starvation resistance in both the laboratory-reared and field-collected ladybirds. The significant differences between the laboratory-reared and field-collected individuals indicate that quantitative conclusions derived from studies investigating solely laboratory-reared individuals cannot be directly extrapolated to field situations.