Periodical Insects

In periodical insects the life cycle has a fixed length of k years and the adults only appear every kth year. Mathematical models have been constructed to investigate the roles of competition between larvae of different ages, predator satiation, and parasitism in leading to periodical behavior. It is shown that periodical behavior results if competition is more severe between than within year-classes, that predator satiation does not lead to periodical behavior in itself but has a powerful effect in reinforcing the tendency of competition between year-classes to lead to periodical behavior, and that parasitism usually leads to an alternating oscillation in which every other year-class is present. It is also shown that predator satiation is likely to be the most important factor in leading to the synchronization of the year-classes in congeneric species of periodical insects. The life histories of three periodical insects (periodical cicadas, May beetles, and the northern oak eggar) are briefly described and interpreted in the light of the theoretical results.