No experimental evidence for host ant related oviposition in a parasitic butterfly

The ability of adult butterflies of the genus Maculinea to locate their host ants prior to oviposition has been the subject of much discussion. We studied the egg laying behavior of the dusky large blue Maculinea nausithous whose larvae parasitize colonies of the ant Myrmica rubra. Flowerheads of the initial food plant were sprinkled with soil from ant nests, which contain chemicals involved in the nest recognition behavior of ants. The experiment was conducted to determine whether ant-released chemicals may act as oviposition cues and whether intraspecific competition for suitable plants may force female butterflies to alternative decisions. Host plant choice was not influenced by the presence of nest-derived host-ant cues. Density dependent shifts to less suitable host plants could not be ascertained nor changes in egg laying behavior across the flight period. The observed egg distribution could be primarily explained by host plant characteristics and environmental variability among sites. The result confirms the theory that host ant dependent oviposition appears to be a disadvantageous strategy in the face of resource limitation within ant colonies and the immobility of caterpillars.