Abstract: Insects have evolved an endogenous biological clock mechanism to synchronize behavioral, physiological and metabolic rhythms with environmental cues, which helps insects to use energy sources more efficiently, thereby conferring an adaptive advantage. The coordinated circadian regulation of behavior, physiology and metabolic cycles is crucial for insects to respond effectively to predictable physiological challenges. Circadian rhythms depend on gene expression to synchronize biochemical processes and metabolic fluxes with the external environment. Circadian clock genes play important roles in some crucial physiological processes such as central and peripheral biological clock mechanism, photoperiod signal transduction, photoperiod-mediated regulation of peripheral tissues, metabolism and immunity. Circadian clock genes are classified into three categories according to their roles: signal transduction-signal input genes, signal oscillation pacemakers and signal output genes. Circadian clock genes constitute complicated transcription-translation feedback loops through interactions with each other and regulate insect circadian and photoperiodic events. This review summarized the identification, classification and functions of circadian clock genes in insects, molecular mechanisms of their action, and the related research methods and challenges. The future research directions were also discussed. This review will provide reference information for further functional research and utilization of circadian clock genes in insects.

Key words: Insect, biological clock, biological rhythm, circadian clock gene, transcription-translation feedback loops, gene function