The circadian system in insects: Cellular, molecular, and functional organization

Abstract The circadian clock organizes the physiology and behaviour of insects to adapt to a daily and seasonally changing environment. The clock oscillates with a period of approximately 24 h in a self-sustained manner, showing an exact 24 h period through synchronization to the daily environmental cycle, and regulates various physiological functions through neural or humoral pathways. These properties of the clock have been extensively studied at molecular and cellular levels in Drosophila melanogaster since the mid-1980s. During the last 2 decades, progress in molecular biology techniques has promoted studies on the clock system in other insects, including higher and lower phylogenetic groups, such as butterflies, honeybees, crickets, and firebrats, enabling us to compare the system, at least in part, among different insect groups.