Social control of division of labor in honey bee colonies

Abstract

Honey bee workers change jobs as they age. By rearing workers under different social conditions and manipulating the age structure of a colony, it was found that workers regulate their onset of foraging through a negative feedback mechanism, which we describe verbally in an ``activator-inhibitor'' model. The level of juvenile hormone (the hypothesized activator) in a worker influences the probability of it becoming a forager. Workers emerge with low levels of hormone, which are programmed to increase. Once the hormone reaches a critical level in a worker, the worker becomes a forager. The level of an inhibitor also becomes high in foragers, and unlike the activator, the inhibitor is transferred from bee to bee so that other individuals are inhibited from becoming foragers. Experimental results support the predictions of this model. Workers become foragers at earlier ages when colonies are manipulated to presumably decrease the levels of inhibitor, and they become foragers at older ages when the levels of inhibitor are increased. Foragers, with high juvenile hormone titers, show a drop in hormone titers when a manipulation is made that presumably increases inhibitor levels drastically. The activator-inhibitor model provides a heuristic tool for understanding the division of labor in honey bee colonies.