Induced indirect defence in a lycaenid-ant association: the regulation of a resource in a mutualism

Indirect defences involve the protection of a host organism by a mutualisti c partner. Threat of predation to the host organism may induce the producti on of rewards and/or signals that attract the mutualistic partner. In labor atory and field experiments we show that threatened lycaenid butterfly larv ae (Plebejus acmon) produce more nectar rewards from their gland and were t ended by protective ants twice as much as controls. Ant attendance did not affect the leaf consumption or feeding behaviour of larvae in the absence o f predators. Inducible nectar production and indirect defence in this syste m may be a mechanism by which larvae provide rewards for services when they are needed the most. Such a system may stabilize the mutualistic associati on between lycaenid larvae and ants by preventing exploitation by either pa rtner.