The cabbage beetle, Colaphellus bowringi, is a short-day species undergoing an imaginal
summer and winter diapause. Its photoperiodic response highly depends on temperature.
All adults entered diapause at </= 20 degrees C regardless of photoperiods. High temperatures
strongly weakened the diapause-inducing effects of long daylengths. The diapause-averting
influence of short daylengths was expressed only at high temperatures (above 20 degrees
C). This indicates that the beetle has a cryptic ability to reproduce in summer. In
fact, summer and winter diapause were induced principally by relatively low temperatures
in the field, whereas photoperiod had less influence on diapause induction. The critical
daylength for the autumnal population was between 12 h and 13 h. By transferring from
a long day to a short day or vice versa at different times after hatching, it was
shown that the sensitive stage with regard to photoperiod was the larva, whereas a
long day was photoperiodically more potent than a short day. The sensitive stage to
temperature encompassed the larval, pupal and adult stages. This different response
pattern serves to ensure that the beetle enters summer and winter diapause in time.
The selections for non-diapause trait under laboratory (at 25 degrees C) and natural
conditions (at >24 degrees C) showed that the beetle could lose its sensitivity to
photoperiod very rapidly.