ABSTRACT
In the humid tropics of SE Asia there are some 14 myrmecophytic species of the pioneer tree genus Macaranga (Euphorbiaceae). In Peninsular Malaysia a close association exists between the trees and the small, non-stinging myrmicine Crematogaster borneensis. These ants feed mainly on food bodies provided by the plants and have their colonies inside the hollow internodes. In a ten months field study we were able to demonstrate for four Macaranga species (M. triloba, M. hypoleuca, M. hosei, M. hulletti) that host plants also benefit considerably from ant-occupation. Ants do not contribute to the nutrient demands of their host plant, they do, however, protect it against herbivores and plant competition. Cleaning behaviour of the ants results in the removal of potential hervivores already in their earliest developmental stages. Strong aggressiveness and a mass recruiting system enable the ants to defend the host plant against many herbivorous insects. This results in a significant decrease in leaf damage due to herbivores on ant-occupied compared to ant-free myrmecophytes as well as compared to non-myrmecophytic Macaranga species. Most important is the ants' defense of the host plant against plant competitors, especially vines, which are abundant in the well-lit pioneer habitats where Macaranga grows. Ants bite off any foreign plant part coming into contact with their host plant. Both ant-free myrmecophytes and non-myrmecophytic Macaranga species had a significantly higher incidence of vine growth than specimens with active ant colonies. This may be a factor of considerable importance allowing Macaranga plants to grow at sites of strongest competition.
ABSTRACT
Many species of the paleotropic plant genus Macaranga (Euphorbiaceae) live in symbiosis with the ant genus Cremastogaster (Myrmicinae), especially with C. borneensis. The ants protect their plants from many herbivorous enemies. The plants provide food-bodies and nesting space in the internodes. In addition the ants care for honeydew producing scale insects in these spaces. The caterpillars of several species of the genus Arhopala (Lycaenidae) parasitize on this symbiosis system. With the aid of their myrmecophilic organs the caterpillars overcome the aggressivity of the ants and feed on the Macaranga leaves without disturbance. Moreover the caterpillars and their pupae are protected against parasites and predators by the ants. As the female butterflies oviposit the eggs only in low numbers upon young leaves, the plants are not seriously affected.The larvae of the three Arhopala species; A. amphimuta, A. moolaiana, and A. zylda are adapted to their host plant species Macaranga triloba, M. hulletti, and M. hypoleuca by means of color, shape, and behavior. In addition, the different larval stages change their appearance according to the parts of the plant on which they feed and rest. These cryptic adaptations point to a distinct monophagy of these butterflies.The state of phylogenetic relationship within the three lycaenids is parallel to the relationship among the three host plants.