Residence period of a flightless strain of the ladybird beetle Harmonia axyridis Pallas (Coleoptera: Coccinellidae) in open fields

Mark-release experiments were conducted to compare the residence period of Harmonia axyridis adults between flightless (selected) strain and control (nonselected) one in small-scale open fields with cultivated eggplants. A flightless strain of H. axyridis was established by artificial selection for reduced flight ability of adults in a laboratory population. Two flightless or control adults per eggplant were released at the center of each experimental plot. Few adults of the control strain were recorded in plots after the release day. In contrast, adults of the flightless strain remained longer on eggplants compared with the control strain in the open fields, even under conditions of low aphid density and a small-scale area. The number of Aphis gossypii was suppressed in plots that contained the flightless strain compared with plots that contained the control strain. These results suggest that the flightless strain of H. axyridis is effective against A. gossypii as a biological control agent in open fields with cultivated eggplants.