Male aggression is caused by a specific pheromone according to researchers at the California Institute of Technology.

Researchers Liming Wang and Michael Maire found that the pheromone 11-cis-vaccenylacetate (cVA) incites the male Drosophila to behave aggressively and hope to be able to take this discovery a step further and explain how aggression is controlled by genetics.

When two male flies were exposed to artificial cVA the frequency at which the flies “lunged” at each other increased significantly. The “lunge” is a term used to describe the behaviour of two opponent males who rear up on their hind legs and snap their forelegs down on top of each other. The pheromone is detected by receptor molecules in the fly’s antenna and a signal is relayed to the brain to promote the behaviour. The flies were able to detect not only their own pheromone but also that of their opponents. The advantage of this is that the number of male flies in a given area remains limited so that there are adequate resources (food and females grazing) to go round the male population. Wang found that by inactivating the receptor, a fly would remain docile.

When the population of male flies reaches a high enough density, the levels of cVA cause the flies to fight and the weaker flies are then chased away. As the levels of cVA fall, the aggression diminishes. Wang describes this behaviour as an advantage because “the population becomes stabilized at an optimal density until more flies become attracted to the food and the cycle repeats itself”.