Explaining extraordinary life spans: The proximate and ultimate causes of differential life Span in social insects: The proximate and ultimate causes of differential life Span in social insects

The striking differences in life span observed among some social insect castes offer unique opportunities to study ageing and have therefore attracted increasing attention. While evolutionary theories of ageing can explain the long life span of social insect queens, experimental evidence to support them is lacking or contradictory. Furthermore, how social insects age is still poorly understood. Senescence patterns vary between behavioural worker castes, and senescence in honeybee workers can even be reversed by inducing a caste transition; but explicit comparisons between queens and workers are needed to understand how queen longevity is linked to senescence. The ability of queens in advanced insect societies to combine long life spans with high investment in reproduction presents a physiological puzzle that may be solved in honeybees by the unique relationship between juvenile hormone and vitellogenin. How this is achieved in other species remains unclear. We finish with a consideration of the challenges facing research into social insect ageing and discuss how these can best be met.