Generalist vs. Specialist Oviposition Behaviour in Papilio Machaon (Lepidoptera) and Functional Aspects on the Hierarchy of Oviposition Preferences

Abstract

Oviposition choice experiments were performed with females from a southern Swedish population of Papilio machaon L. The results show that the females had a hierarchy of oviposition preferences which were in accordance with the suitability of the plants as food for the larvae. There was little variation between females in hierarchical ranking of host plants. However, variation between females was profound with respect to differences in thresholds of acceptance of alternative plants. Thus some females exhibited a generalist oviposition choice strategy and laid eggs on several plants even when the optimal host plant was available, whereas others exhibited a specialist strategy and restricted their egglaying to the optimal host plant as long as it was available. Generalist females also had a tendency to lay eggs on plants that were unsuitable as food for the larvae, whereas specialist females avoided to lay eggs on such plants. It is suggested that the hierarchical arrangement of oviposition preferences may have a dual function, viz. both to ensure that most eggs are laid on the optimal host plant as long as it is present, and make possible the deposition of eggs on sub-optimal host plants when the optimal plant is absent. Thus, the preferential hierarchy may be the mechanism which effects conservatism in host plant choice in habitats to which the butterflies are adapted, and also makes possible innovative change in host plant utilization in novel habitats where the familiar host plants are absent.