Natural daylengths regulate insect seasonality by two mechanisms.

Abstract

FOR many animal species in temperate regions of the world, the photoperiod is the major environmental factor that reliably signals forthcoming seasonal changes. With the exception of studies dealing with several species of birds1,2, experiments generally have not shown what features of the natural photoperiod are used by animals to perceive calendar time. Not only have investigations of photoperiodicity usually used stationary photoperiods in the laboratory, but generally they have not taken into account the seasonal variations in the rate of change in the length of the day3; these changes are greatest at the time of the equinoxes and smallest at the time of the solstices. Our results demonstrate for the first time that insects have evolved at least two mechanisms based on seasonal changes in photoperiod to end diapause at the end of winter.