DUELING APHIDS - INTRASPECIFIC FIGHTING IN ASTEGOPTERYX MINUTA (HOMOPTERA, HORMAPHIDIDAE)

The function and consequences of fighting behaviour in the horned aphi d Astegopteryx minuta were investigated. Individual aphids fought each other for feeding sites on bamboo leaves: if the attacker won, it ins erted its stylets into the precise site on the leaf from which the def ender had just withdrawn its stylets. This feeding site, demarcated by a collar ca 50 mu m in diameter, represents perhaps the smallest know n territory amongst the insects. The mean duration of the duels +/- SE was 3.3 +/- 0.3 min (range 0.3-13.3, N=64). Most duels (92%) were won by the larger aphid, and long fights occurred only when the participa nts were evenly matched in size. The aphids used three strategies to s ecure a feeding site: they could dislodge another aphid by fighting, u se a feeding site previously abandoned by another aphid, or insert int o a virgin area of leaf. Adult aphids almost always fought, first inst ars very rarely fought, and roughly half the third instars fought. Usi ng a pre-existing feeding site, gained either by fighting or by using an abandoned site, conferred significant time benefits: an aphid took four to five times longer to secure a feeding site on a virgin leaf th an on a crowded or a used leaf. The presence of other aphids significa ntly altered their searching behaviour. This duelling behaviour might be the evolutionary forerunner of anti-predator defensive behaviour, a lthough it is paradoxical that the stage that becomes specialized as t he warrior morph, the first instar, is the stage that was originally t he least likely to fight other aphids for a feeding site. (C) 1996 The Association for the Study of Animal Behaviour.