Abstract: Autophagy is a ubiquitous phenomenon of intracellular selfdegradation in living organisms. In order to recycle cellular substances during autophagy, cytoplasmic aggregates and organelles are engulfed into doublemembrane autophagosomes and finally delivered to lysosomes for degradation. Autophagy is initiated as an adaptive response for cell survival in unfavorable conditions, such as starvation, anoxia, endoplasmic reticulum stress, pathogen invasion and aggregation of dysfunctional proteins, while extensive autophagy can act as an initiator and executor of programmed cell death (PCD). Although the molecular assembling of autophagosomes and induction of autophagic pathway have been extensively documented, it is hard to reach a consensus on some important issues. In this review, we summarized and discussed the biological significance of the occurrence of autophagy and the source of autophagosomal membrane in insects. Under the circumstance of mild starvation, low level of autophagy will be induced to activate basal metabolism and to maintain cell survival. Challenged with excessive starvation during the feeding phase or stimulated by ecdysone during metamorphic development, high level of autophagy and apoptosis are triggered in larval tissues which will undergo irreversible cell death. Starvation causes delays of larval growth and development and eventual lethality, while 20E result in molting and degradation of larval tissues. Different from the pioneering studies in yeast and vertebrates, there are still not enough documented evidences to address whether pathogenic invasion can stimulate low level of autophagy in insect cells. The issue that almost all of the organelles-derived membrane can serve to be the source of autophagosomal membranes remains to be further investigated.

Key words: Insect, autophagy, biological function, autophagosomal membrane, programmed cell death