Change in photoperiodic sensitivity during larval development of Pieris brassicae

Sensitivity to light/dark cycles in Pieris brassicae starts with the second larval stage at a low level, reaches a maximum 1–2 days after the moult to the last larval stage, and then decreases rapidly to zero just before pupation. This peak in photoperiodic sensitivity is an invariable character of the species. It is not affected by temperature or by the strength of the photoperiodic signal, nor does it vary between different populations. This age-dependent sensitivity is a scarcely noticed quantitative component in arthropod time measurement. This study discusses, whether the change in photoperiodic sensitivity is an adaptation to minimize the risk of taking the wrong developmental pathway in late summer.