A potential risk and management of feces in the queenless ant

Many ant species inhabit closed environments with limited spaces underground, encompassing a potential risk of pathogen reservoir and transmission among colony members. Despite accumulated research on the triggers of endemic outbreaks, the mechanism through which pathogenic microorganisms are introduced into ant colonies from outside the nest remains unclear. Waste materials could be one of the potential sources of pathogens, and we hypothesize that the feces of infected foragers may serve as a route of pathogen infiltration into the nest. In this study, we examined the transmission route and distribution pattern of an entomopathogenic bacterium, Pseudomonas entomophila, and ant behaviors in the nest using Diacamma cf. indicum from Japan. First, through infection experiments, we revealed that infected foragers introduce foreign pathogens into the nest via their feces, and the distribution of introduced pathogens within the nest shows a bias towards the midden room. Subsequently, our behavioral observations showed that reproductive individuals tend to remain in the other nest rooms. Overall, our results suggest that while the feces of infected foragers are potential reservoirs of disease outbreaks within a colony, such a risk might be mitigated by confining feces in a specific room of the ant nest.