Ants as Selective Agents on Herbivore Biology: Effects on the Behaviour of a Non-Myrmecophilous Butterfly

Abstract

Larvae of the nymphalid butterfly Eunica bechina feed on young leaves of Caryocar brasiliense, a shrub of the Brazilian savannah that is frequently visited by nectar-gathering ants. Eggs are not removed by ants, but ant occupation on plants affects the oviposition behaviour of the butterflies. Adult females avoid laying eggs on highly visited plant locations and visual cues were demonstrated to mediate oviposition by the butterflies. Plant branches with artificial rubber ants were significantly less infested than control branches with rubber circles. This is the first demonstration that ant presence per se can be enough to produce an avoidance response by ovipositing females in a non-myrmecophilous butterfly. Larval mortality was strongly affected by the level of ant visitation to the host plants, and vulnerability to ant predation decreased with larval size. Stick-like frass chains constructed by the larvae at leaf margins were demonstrated to be a safe refuge against ant attacks on the host plant. Live termites placed on leaves were attacked by foraging ants in significantly greater numbers than those placed on the frass chains. It is concluded that the behavioural biology of both immature and adult Eunica bechina is finely linked with the utilization of a host plant where ant visitation patterns strongly affect larval survival.