RITUALIZED VERSUS AGGRESSIVE BEHAVIORS DISPLAYED BY POLYRHACHIS-LABORIOSA (SMITH,F.) DURING INTRASPECIFIC COMPETITION

The intraspecific territoriality of Polyrhachis laboriosa was studied thanks to dyadic confrontations between nestmates and alien foragers i n chemically marked and unmarked arenas, complementing experiments and observations in nature. When foragers meet, the alien flees while the resident attacks, especially when on a marked area. However, when an alien scout extends its territory, it attacks the resident ant, such c onfrontation resulting in a high rate of reciprocal full attacks. When surrounded by several residents, the intruder is always spread-eagled if it does not succeed in fleeing. We described ritualised displays, such as threatening (opening mandibles; bending the gaster) or appeasi ng behaviours (antennal boxing; attempt at trophallaxis; pupal posture raising the gaster). They occur only when the encounter maintains a l ow level of aggression, during laboratory experiments, or in nature du ring encounters involving a queen or an experimentally-introduced intr uder. Foraging queens are tolerated on the territories of conspecific mature colonies. When they encounter resident workers, reciprocal avoi dance occurs. Nevertheless, the latter perform ritualised displays whe n the queens approach their nest or attempt to rob their prey. This si tuation seems to compensate in part the archaic semi-claustral mode of foundation of this species, as the queens are indirectly protected by their conspecifics who do not tolerate other competitors around large food sources. (C) 1997 Elsevier Science B.V.