LONG LIFE-CYCLES IN INSECTS

Several insect species have life cycles that last more than 1 year, because of very slow growth, repeated or prolonged dormancies, or very long lived adults. These long life cycles are correlated with environmental adversities, such as cold or unpredictable temperatures, patchy, unreliable or low quality food supplies, and natural enemies, as well as with some other properties such as large size. Long life cycles are most prevalent when several of these factors are present simultaneously. Adversities tend to prolong the life cycle of all individuals in the population, whereas unpredictability tends to extend the life cycle of only some individuals. Extreme extensions, such as diapause for more than 10 years, usually affect only a very small fraction of the population. Modest extensions, such as development over 2 years, prolonged dormancy for one additional adverse season, cohort-splitting between 1- and 2-year life cycles, and oviposition over two seasons, are relatively common. Insects with long life cycles provide insights into the nature of adaptations to adverse and unpredictable conditions, and also provide useful material for the analysis of questions related to population and community structure.