Overwintering ability of a flightless strain of the ladybird beetle Harmonia axyridis (Pallas) (Coleoptera: Coccinellidae)

Abstract

We examined the overwintering ability of a flightless strain of the ladybird beetle Harmonia axyridis (Pallas) (Coleoptera: Coccinellidae), which is used as a biological control agent for aphids. The flightless strain was established via artificial selection for reduced flight ability and with no exposure to cold temperature (winter) during the selection. To examine the overwintering ability of the flightless strain, the survival rates were compared with those of wild strains under low temperature laboratory conditions and field winter conditions. In the laboratory experiment, survival rates of flightless strain individuals directly transferred to 5 °C were significantly lower than those with low temperature acclimation. Effects of aggregation on the survival rate at 5 °C were not confirmed. No significant differences were detected between the flightless strain and a wild strain originated from Saga, Kyushu, Japan. In the field experiment, winter survival of the flightless strain was significantly lower than the wild strain both in males and females while not significantly different from another wild strain originated from Fukuyama, Honshu (close to the original locality of the flightless strain). These results suggest that the artificial selection for reduced flight ability did not affect the overwintering ability of H. axyridis.