Studies on the south east Asian ant-plant associationCrematogaster borneensis/Macaranga: Adaptations of the ant partner

Abstract

C. borneensis (Myrmicinae) lives in close association with several myrmecophytic species of the South East Asian pioneer tree genusMacaranga (Euphorbiaceae). The ants are adapted to the plants so closely that they do not survive away from it. The only food they utilize is provided as food bodies by the plant and honeydew from specific scale insects kept inside the hollow internodes. The anatomy of the digestive tract is also adapted to life on the host plant: the crop is very small and can store only minute food quantities. C. borneensis exclusively colonizes certainMacaranga species. Queens as well as workers are able to recognize their host plant species, probably by chemical cues. Colony founding queens swarm throughout the year, mostly during darkness. There is strong competition among queens for host plants. Queens do not carry scale insects on their nuptial flight. Worker ants are active day and night. Most of them patrol and collect food bodies on the younger parts of the host plant. An important characteristic is their cleaning behaviour, which results in removal of all foreign objects. Even though they are rather small, workers respond very aggressively to certain kinds of disturbance of the host plant. The ants attack most phytophagous insects and are especially effective in killing and removing small, softbodied herbivores (e.g. caterpillars). They do not possess a functional sting, but apply defensive secretion and—once biting an intruder—will not let go. Their effective alarm system results in a mass attack, which provides adequate defence for the colony and the host plant. A comparison with anotherCrematogaster species further illustrated the special adaptations ofC. borneensis to its host plant.