LIFE-CYCLE PATHWAYS AND THE ANALYSIS OF COMPLEX LIFE-CYCLES IN INSECTS

The structure and temporal control of insect life cycles can best be understood by viewing them as pathways along which various options (e.g. develop or enter diapause; grow rapidly or grow slowly) are chosen in response to environmental controls such as photoperiod and temperature. Simple life cycles include small numbers of such options. The combination of several successive simple elements, however, can produce remarkably complex life cycle patterns, which are more prevalent than most entomologists have recognized. The ways in which these simple elements contribute to life cycle pathways are outlined and illustrated schematically. Flow charts showing the successive decision points in the life cycle then are constructed for selected species. This approach confirms the different simple elements, and shows how they are used in combination to control seasonal life cycles in nature.