Researchers at North Carolina State University in the US have identified a specific chemical on the exoskeletons of royal termites that they believe allows worker termites to recognise royal status. (Main photo credit: Dann Thombs)
Researchers at North Carolina State University in the US have for the first time identified a specific chemical used by the higher termite castes – the queens and the kings – to communicate their royal status with worker termites. The findings potentially advance our knowledge of termite behaviour and the evolution of social insects.
For social insects, such as termites and insects of the order Hymenoptera (ants, bees and wasps), chemical communication using pheromones is vitally important to the success of the colony, as it allows nestmates to recognise each other. It is well documented that some pheromones are caste-specific, meaning a particular cuticular hydrocarbon (CHC) may only be found on the exoskeletons of workers, or soldiers, for example. This allows an insect to recognise not only nestmates, but also recognise the caste to which another fellow insect belongs.
In the study published in Proceedings of the National Academy of Sciences, co-authors Professor Coby Schal and PhD graduate Colin Funaro used gas chromatography to isolate specific chemicals on the exoskeletons of royal and worker Reticulitermes flavipes termites.
They discovered heneicosane – a wax-like hydrocarbon, consisting of only carbon and hydrogen atoms – on body surface of the royal termites, but not on workers. It is the first time a royalty-recognition pheromone has been identified.
Worker response to fake royals
The researchers used glass dummies serving as royal termite proxies and treated the dummies with various extracts to test the reactions of the other termites. As a control, the researchers treated the dummies with worker extract alone.
When the researchers treated the dummies with a blend of worker extract and heneicosane – the CHC found on the exoskeleteons of the royal termites – worker termites exhibited increased levels of shaking, a behaviour they tend to exhibit naturally in the presence of reproductives. They showed both lateral and longitudinal shaking behaviour and also increased antennation.
The termites demonstrated significantly lower levels of shaking towards the dummies treated with worker extract.
“Termites use a two-step recognition process – the colony’s odour gives workers a ‘home’ context and heneicosane within this context denotes ‘royals are in the home’,” explained Professor Schal.
Mr Funaro added, “The royal-recognition pheromone lets workers know that there is a queen or a king present and that everything is stable in the colony. Worker termites shook more when realising that the royals were also nestmates.”
The researchers believe that the presence of heneicosane on the royal termites’ exoskeletons allows worker termites to recognise and care for them, which serves to maintain order within the colony.
A question of evolution
The study calls into question the widely held belief that queens of the insect order Hymenoptera were the first to use these wax-like hydrocarbon pheromones for royal recognition.
Termite colonies are unusual in that they are founded by a monogamous kind and queen pair of primary reproductives, whereas in social Hymenopteran colonies, males have only a transient presence. “This is the first report of a queen recognition pheromone in termites and the first report of a king recognition pheromone in insects,” said Professor Schal.
“Termites appeared some 150 million years ago while the social Hymenoptera appeared about 100 million years ago, so this discovery of a hydrocarbon as a royal-recognition pheromone in termites appears to predate its use in social insects,” Professor Schal said.
The researchers believe further study should investigate deeper as to whether king and queen termites in fact have their own sex-specific pheromones. The shaking response could also be explored further, as although the shaking behaviours are widely seen throughout the colony of most termite lineages, a deeper investigation could broaden our understanding of termite behavioural patterns.
The discovery of this royalty recognition pheromone also gives rise to a number of questions as to how this, and other unidentified pheromones, may control worker behaviour and the development of reproductives within the colony – functions that are controlled by pheromones in the Hymenoptera.
More termite information
Source: North Carolina State University. ‘Termite queen, king recognition pheromone identified’. ScienceDaily, 19 March 2018.
Journal reference: Colin F. Funaro, Katalin Böröczky, Edward L. Vargo, Coby Schal. ‘Identification of a queen and king recognition pheromone in the subterranean termite Reticulitermes flavipes’. Proceedings of the National Academy of Sciences, 2018; 201721419.