Basic biology of an invasive ant pests: Intraspecific aggression and longevity in the dark rover ant (Brachymyrmex patagonicus)

The dark rover ant (Brachymyrmex patagonicus Mayr) is an invasive species that has recently expanded its range through the southern US. Its recent success as an invasive species and structural pest raises questions about the biology and behavior of this little known species. In urban environments, B. patagonicus frequently has high population densities with several nests close to each other. One concern is that these ants might form supercolonies of interconnected nests without aggression among each other. We assessed this possibility using dark rover ants collected from the field. We paired ants from different colonies inside glass vials and ranked the aggressive interactions between each pair. This procedure was repeated using ants from colonies far apart and in close proximity with each other. We found high levels of aggression between ants from different colonies. This makes it unlike that rover ants might form supercolonies. However, when colonies a few meters apart were considered, aggressive interactions were less frequent. We also assessed the long term survival of colony fragments separated from their parent colonies. If colony fragments are able to survive after the death of their parent colony, pest reemergence might occur after apparent control.  We maintained eight small, queenless colony fragments under laboratory conditions and recorded the mortality of ants monthly. All the colony fragments were able to survive for over a year, and the longevity of 2 of them exceeded 18 months. This remarkable longevity might be behind some of the difficulty in the management of this species.