Photoperiodic time measurement, photoreception, and circadian clocks in insect photoperiodism

Photoperiodism is an adaptive response used by organisms to assess day length and anticipate upcoming seasons and to coordinate their (or their offspring’s) development and physiology with the environmental changes. These physiological mechanisms have long been studied to understand insect life cycles, combat pests, conserve endangered species, and rear beneficial insects. Recent genetic manipulations have greatly expanded our knowledge of the molecular mechanisms underlying photoperiodism. Here, I review our current knowledge of the physiological and molecular mechanisms underlying photoperiodic time measurement, photoreception, and circadian clocks, which constitute insect photoperiodism modules, with a special emphasis on photoperiodic time measurement models.