Reversion in honeybee, Apis mellifera, workers with different life expectancies

Under the age-related division of labour of a honeybee colony, workers participate first in safe inside-nest tasks and then switch to risky outside-nest foraging. However, honeybees show great plasticity during behavioural development: their hive-to-field transition can be accelerated, delayed or even reversed in response to changes in colony conditions or environmental factors. After nursing bees are removed from a colony, younger foragers are more likely to revert to nursing than older ones. The ‘division of labour by division of risk’ hypothesis predicts that it is not the workersʹ age but their life expectancy that influences whether or not foragers return to inside-nest activity. We tested this prediction by dividing same-age honeybee workers into three groups after they started foraging. Workers in the control group were not treated. The life expectancy of the other two groups was shortened with carbon dioxide anaesthesia or by injury. In a cage experiment we showed that control bees had a longer expected life span than anaesthetized and injured workers, while in a field experiment the control workers, with a longer expected life span, proved more likely to revert to nursing than anaesthetized and injured workers of the same age. Behavioural reversion was accompanied by ovary development and hypertrophy of the hypopharyngeal glands. These results support the tested hypothesis that the division of labour in eusocial insects is a consequence of differences in expected worker life span and differences in the risks associated with inside-nest and outside-nest tasks.