COMPETITION, TERRITORIALITY AND MATERNAL DEFENSE IN A GALL-FORMING APHID

This study reports on the aggressive behavior of the gall-forming aphi d Smynthurodes betae West. Videotaped behavior and experiments demonst rated that first instar offspring of the fundatrix protect their galli ng sites against conspecific competitors (the larger individuals win), as well as against first instar competitors of the sympatric galling aphid Forda riccobonii (Steph.). In mature galls, adult aphids also pr otect their gall and their offspring from conspecific invaders and nat ural enemies. The fighting behavior of the adult aphid is unique: the aphid seizes the intruder while lying on its back, enabling use of all six legs and the mouthparts. This is the first documentation of aggre ssive defensive behavior by adult aphids. Although the aggressive beha vior of the adult aphid protects the gall and offspring, no distinct p arental care behavior was observed. The territoriality and aggression are highly adaptive because of the limited number of galling sites. Un der natural conditions, removal of the adult aphids from the galls res ulted in significantly increased invasion by conspecific intruders. Th e results indicate that the role of interspecific competition and natu ral enemies in shaping adult behavior is rather limited. The open gall s and the unique life-cycle of S. betae encourage and prolong intraspe cific competition and facilitate confrontations between adults and inv ading nymphs. The ability of the adult owner of the gall to prevent in vasions of nymphs has promoted the evolution of maternal defense in th is aphid. This study supports the hypothesis that galls, as high Value resources that combine food and shelter, are often associated with de fensive and social behavior.