Abstract: To understand the nature of photoperiodic time measurement in the induction of summer diapause of the cabbage beetle, Colaphellus bowringi Baly, the incidence of summer diapause of C. bowringi under different long day-lengths and the number of light-dark cycles required to induce 50% individuals to enter summer diapause at 25℃ was investigated in the laboratory. The results showed that the incidences of summer diapause induced by different long day-lengths were different significantly. The incidence of diapause induced by day-length of 15 h or 16 h was the highest, and the incidence of diapause significantly declined when the day-length was longer or shorter than 15 h or 16 h. In the transferring experiments of different light-dark cycles, the incidence of diapause induced by the day-length of 14 h did not exceed 50%. The number of light-dark cycles required to induce 50% individuals to enter summer diapause was 2.61 d at L15∶D9, 3.72 d at L16∶D8, 4.64 d at L17∶D7 and 5.92 d at L18∶D6, showing significant differences between the treatments. The results suggest that the induction of summer diapause in this beetle is based on a quantitative photoperiodic response.

Key words: Colaphellus bowringi, diapause, diapause induction, photoperiod, summer diapause, quantitative reaction