Juvenile hormone triggers forager switch in leafcutter ants

It takes all sorts of characters to build a city, and insect colonies are not that different from our own metropolises. Some residents perform caring roles while others provide defence or infrastructure, although few insects stay in a role for life. For example, honeybee workers perform a wide range of tasks – from cell cleaning and nursing when young to foraging in later life – and many of these transitions are controlled by juvenile hormone, which regulates growth. However, Victoria Norman and William Hughes, from the University of Sussex, UK, explain that little is known about the role of juvenile hormone in defining a place in society for other insect species. ‘Direct experimental evidence for the influence of juvenile hormone outside of the honeybee model system is lacking’, they say. So, the duo decided to find out how doses of juvenile hormone affect the behaviour of leaf-cutting worker ants.Having gently applied six minute dabs of juvenile hormone to the back of young nurse ants over the course of a fortnight, Norman tested how the hormone affected each insect's behaviour by filming their activity and was impressed to see that they were significantly more active than ants that had received a dab of fake hormone. And when she tested their response to light, the hormone-treated ants were much happier spending time in the light, while the untreated ants preferred to shelter in the dark. Next, Norman checked the hormone-treated ants’ reactions to an imposter by touching their antennae against the body of an ant from another species and found that the hormone-treated ants were much more aggressive towards the trespasser than towards the untreated ants. And finally, when Norman introduced the hormone-treated ants into a mini nest full of workers tending fungus, the hormone-treated ants had no interest in sticking around to help with the cultivation, preferring to head out of the nest instead. The workers were behaving more like foragers, while the ants that had not received juvenile hormone treatment continued behaving like nest-bound workers. In short, juvenile hormone seemed to have caused the workers to transform from timid workers into fierce, more outgoing foragers.‘This is the first experimental evidence of the effect of juvenile hormone on division of labour in ant societies’, say Norman and Hughes, and they add, ‘This suggests that juvenile hormone may have a highly conserved role as a key endocrine mediator of division of labour within eusocial insect societies that has been key to their ecological and evolutionary success’.