What worker bees do depends on how old they are. A worker a few days old will become a nurse bee that devotes herself to feeding larvae (brood), secreting beeswax to seal the cells that contain brood and attending to the queen. 

After about a week, she will progress to other tasks, such as grooming nest mates, ventilating the nest and packing pollen. Only at the end of her life will she become a forager, venturing forth to collect nectar and pollen for the colony.

Yehuda Ben-Shahar, PhD, assistant professor of biology in Arts & Sciences at Washington University in St. Louis, wondered if this highly stereotyped system of task allocation wasn’t somehow under genetic control.

In an article published in the advance online edition of Genes, Brain and Behavior on April 6, 2012, he and colleagues from Washington University, the University of Delaware, the University of Illinois Urbana-Champaign and the Institute for System Biology in Seattle, demonstrate that the division of labor among honey bees coincides with the presence in their brains of tiny snippets of noncoding RNA, called micro-RNAs, or miRNAs, that suppress the expression of genes.

Forager bees that venture out to collect nectar and pollen have higher levels of some miRNAs in their brains than nurse bees that are devoted to tending to brood.

By comparing honeybee miRNAs to those of wasps, bees and ants, the scientists also showed that eusocial insects share many miRNAs that are absent in solitary insects. (Eusociality is an extreme form of social organization in which organisms care for young communally and give up reproductive rights to a queen.)

The pattern of conservation across species suggests that miRNAS, are important regulators of social behavior not just during the bee’s lifetime but also over evolutionary time.

Working for a living

Worker bees become foragers only at the very end of their lives, after making their way through a list prescribed tasks from feeding brood to ventilating the nest. The forager in this photo is recognizable by her saddlebags, which are stuffed with yellow pollen.

Ben-Shahar chose the honeybee (Apis mellifera) as his model organism for the genetic control of behavior because the worker bees display such well-characterized division of labor.

Task allocation in honey bees is highly scripted, and yet the script is flexible enough to respond to labor shortages. If there aren’t enough nurse bees in the colony, nurses will stick with their tasks past the usual age limit, becoming what are called overage nurses. And if there aren’t enough foragers, bees too young for that role will rush to take it on, becoming precocious foragers.

For the scientists this plasticity makes bees a very powerful behavioral model. By comparing overage nurses to precocious foragers it is possible to compare gene expression in different behavioral states without the confounding factor of age.