Photoperiod at the larval stage sets the timing of entire annual program in an herbivorous insect

To maximize their fitness, organisms need to synchronize their phenology with the seasonal variation in environmental conditions. Most phenological traits are affected by environmental abiotic cues such as photoperiod, temperature and rainfall. When individuals with complex life-cycles fail to match one of the stages with the favourable environment, these negative conditions experienced may lead to carry-over effects and, thus, influence fitness in subsequent stages.
In the winter moth, an herbivorous insect with an annual life-cycle, timing of egg-hatching in spring is strongly influenced by temperature and varies from year to year. To investigate whether the phenological variation in egg-hatching date affects subsequent stages, we analysed data on egg-hatching and adult catching date (considered here to be a proxy for adult eclosion date) from our long-term study (1994-2014). Furthermore, we experimentally manipulated the photoperiod experienced by newly hatched larvae and recorded t...