For Indian jumping ants (Harpegnathos saltator), becoming royalty is all about timing.
If a larva shows signs of becoming a queen at the wrong time, it is physically harassed to remain a humble worker. But the same cues at the right time give the larva access to the resources it needs to thrive and develop as a queen. Now scientists have identified the “princess pheromone” that tells a colony when an ant larva is aiming for coronation.
“People have been studying pheromones in ants for over 50 years, and pretty much everything we’ve learned concerns how adult ants use pheromones to communicate with each other,” said Clint Penick, a postdoctoral researcher at North Carolina State University and lead author of this paper. study. “This is one of the few cases — maybe even the first time — that we’ve found ant larvae that produce pheromones that influence colony behavior.”
Each year, around the time of the first summer rains, colonies of H. saltator breed the latest crop of queens, which leave their colonies after reaching adulthood and embark on a mating flight. The queens breed with winged males and then establish their own colonies.
However, if an ant larva indicates that it is developing into a queen at the wrong time of year, such as the middle of winter, that is a problem. The timing is all wrong for a mating flight, and the larva would use colony resources for no reason. So when worker ants detect an emerging queen at the wrong time, they chew on it. Literal. The stress caused by the bite of the larva encourages the larva to develop as a worker.
“Workers can also prevent queen development if more queens develop than the colony can support,” Penick says. “In the same way, when released at the right time, the princess pheromone allows workers to facilitate the development of the next generation of queens.”
The researchers were able to see that some sort of non-visual signal relayed information from H. saltator larvae to workers based on observations of how worker ants interacted with seemingly identical larvae.
To investigate, the researchers examined the wax coating found on the cuticle of larvae. Specifically, they sampled the wax coating of large larvae that were clearly about to become queens and of smaller larvae that were likely to become workers. They found that the chemical composition of the different wax layers was clearly distinguishable.
The researchers then experimented by transferring the wax layer of queen larvae to the cuticle of worker bee larvae. The presence of spores from the queen larvae was sufficient for the workers to react to the small worker larvae as if they were developing into queens.
In addition, by treating worker larvae with a hormone known to trigger queen development, the researchers were able to get the larvae to produce the princess pheromone. This also happened when the hormone was given to male larvae; the males would produce the princess pheromone even though they were unable to develop into queens. The presence of the pheromone alone was sufficient to provoke aggressive behavior of the workers, even towards male larvae.
“Signals like the princess pheromone are essential for social insects,” Penick says. “Ants have to have a way of making sure there are enough workers in the colony, otherwise all the larvae could develop as queens and the insect community would break down. Instead of ants, you’d have more of a wasp colony.
“This work sheds light on how castes are differentiated in this species and gives us more insight into the complex evolutionary biology behind social insect behavior,” Penick says. “Since H. saltator is from one of the older genera of ants, this mechanism is probably quite common in social insects — but more research needs to be done to determine if princess pheromones are present in other species.”
Video of workers attacking these larvae can be seen at https://vimeo.com/212090021.