Interspecific Difference in Response to Change in Ant-Defense Intensity during Tree Growth among Three Leaf-Chewing Lepidopteran Species on a Myrmecophyte Species, Macaranga bancana

Myrmecophytes of the genus Macaranga (Euphorbiaceae) have symbiotic relationships with specific ant species in which ants protect the host plant from herbivores. The intensity of such anti-herbivore defenses elicited by symbiotic ants has been shown to decline with the increase in tree size during tree growth and drastically decrease with various types of disturbances, such as tree falls and ant predation during tree growth. These decreases in anti-herbivore defense during tree growth may cause differences in host plant utilization among leaf-chewing lepidopteran species that vary in the degree of development of myrmecophilous traits. In this study, to test this hypothesis, we determined the interspecific differences in host plant use response to tree size variation and the absence or presence of symbiotic ants among three dominant leaf-chewing lepidopteran species, a myrmecophilous species (Arhopala amphimuta), and two non-myrmecophilous species (Shafferiella macarangae and Aetholix flavibasalis) feeding on a Macaranga myrmecophyte species, M. bancana, in a primary forest in Borneo. The results showed that there were significant differences in the responses to the absence or presence of symbiotic ants and tree size among the three lepidopteran species. The literature has suggested that the larvae of myrmecophilous species prefer trees with symbiotic ants. Although larvae of the non-myrmecophilous S. macarangae were found on trees with and without symbiotic ants, the moth species may prefer trees with weak anti-herbivore defense intensity. We identified another non-myrmecophilous species, A. flavibasalis, that used M. bancana trees as host plants only when symbiotic ants were no longer present on the trees. These results support our hypothesis and suggest that changes in anti-herbivore defense intensity associated with the growth of Macaranga myrmecophytes have a strong influence on host plant usage by lepidopteran leaf chewers.