Research has identified a mechanism by which young, terminally ill ants (pupae) prevent the spread of disease within their colonies. These pupae emit a specific chemical signal that prompts adult worker ants to eliminate them through a process termed "destructive disinfection."
Ant colonies, characterized by high population density and genetic similarity among individuals, are environments conducive to rapid disease transmission. To counter this, ants have developed various disease defense strategies, collectively referred to as social immunity. Examples include nest restructuring to inhibit fungal spread and queens consuming infected brood.
Previous research led by Sylvia Cremer, a professor at the Institute of Science and Technology Austria, identified "destructive disinfection." In this process, worker ants unwrap the cocoons of sick pupae and apply a self-produced disinfectant, which leads to the pupa's death. This action occurs before the pupa becomes infectious to other colony members.
The current study, a collaboration between Cremer's group and chemical ecologist Thomas Schmitt from the University of Würzburg, investigated whether the pupae actively signal for this disinfection. The invasive garden ant species Lasius neglectus was used for the research.
Experiments showed that sick pupae emitted the chemical signal only when adult worker ants capable of performing destructive disinfection were present. This suggests a strategic allocation of resources by the pupae for signal production. Furthermore, the signal was observed in young worker pupae but not in queen pupae, as young queens are capable of resisting infection.
To confirm the causal relationship, researchers transferred the chemical signal from sick pupae to healthy pupae. When these scent-transferred healthy pupae were placed with adult worker ants, the workers initiated the disinfection process, including unpacking the cocoon. This demonstrated that the chemical signal directly triggers the destructive behavior in worker ants.
Researchers Neil Tsutsui and Sylvia Cremer note that while the behavior might appear altruistic, it is consistent with the indirect perpetuation of genes. Given that most worker ants are sterile, the elimination of a sick individual can safeguard the genetic lineage of the colony, thereby contributing to the transmission of shared genes through surviving relatives.