Influence of caste polyethism on longevity of workers in social insect colonies

Different patterns of division of labor can affect the expected longevity of social insects workers. It has been earlier suggested that when tasks performed inside and outside colony are equally risky then the expected longevity of workers in colonies with caste polyethism is greater than that in colonies without polyethism. To verify these predictions I used a model assuming two sets of tasks, associated with different mortality rates. In the colony without polyethism the workers preformed safe and risky tasks in turn, while in the colony with caste polyethism the workers specialized in only one set of tasks. The outcomes suggest that the expected longevity of workers in colonies with caste polyethism cannot be greater than that in colonies without polyethism. Only if there is no aging and under some special and rare conditions are there no differences in expected longevity between colonies with and without caste polyethism. If aging is independent of activity, caste polyethism does not shorten longevity when all tasks in the colony are equally risky. The results can explain why caste polyethism is not as widespread among social insects as age polyethism.