Adult eclosion rhythm of the cabbage moth, Mamestra brassicae, pupating in the soil, was recorded in darkness under two thermoperiods, 24°C (12 h):16°C (12 h) and 20.5°C (12 h):19.5°C (12 h), with different amplitude and the same average temperature. Clear daily rhythms of eclosion were observed in both conditions. However, moths eclosed about 2 h before the temperature drop in 20.5°C:19.5°C, but 4 h later in 24°C:16°C. This response to the amplitude of temperature cycle, together with similar previous observations of adult eclosion rhythms in dipterous insects, might suggest a widespread means of adaptation among insects pupating in the soil to compensate for the depth-dependent phase delay of the temperature cycle, which is the only time cue available in the soil.