Wednesday, December 12, 2007 - 11:17 AM

Sustained contact reduces aggression between adjacent Argentine ant supercolonies

Alexei Rowles, and Jules Silverman, North Carolina State University, Entomology, 3321 Gardner Hall, Box 7613, Raleigh, NC

Throughout their introduced range, Argentine ants form expansive colonies (supercolonies) due to a lack of behavioral boundaries over large spatial scales. Intraspecific aggression has been demonstrated between geographically separate and genetically distinct supercolonies, but less is known about the interactions that occur on the boundary between contiguous supercolonies. Given the costs often associated with territorial boundaries, such interactions are likely to provide insights into how supercolonies are maintained. Using Argentine ants collected from transects replicated across a boundary between two supercolonies, aggression assays were conducted in the laboratory to assess the effect of contact upon intensity of aggression. Intraspecific aggression between supercolonies was measured by pairing ants from the immediate boundary, 100 meters away and with another, non-adjacent supercolony. This allowed comparison of aggression relative to different histories of interaction. Aggression between colony pairs was measured before connection and at intervals after wards. Control pairs remained unconnected. Throughout all colony pair combinations, high aggression prior to connection was nearly absent after two days of interaction. No queen movement occurred and aggression assays between experimental pairs and source colonies revealed intact colony separation. Results initially suggest the occurrence of the Dear-Enemy phenomenon. However, they contradict similar studies and the ongoing field condition where a territorial boundary between supercolonies is continually maintained. Further interaction experiments emulating field conditions aim to determine how ongoing boundaries between supercolonies are supported.

Species 1: Hymenoptera Formicidae Linepithema humile (Argentine ant)