Food plant selection by stick insects (Phasmida) in a Bornean rain forest

Abstract

Stick insects (Phasmida) are important herbivores in tropical ecosystems, but have been poorly investigated in their natural environment. We studied phasmids and their food plants in a tropical lowland rain forest in Borneo (Danum Valley, Sabah, Malaysia). Thirty species of phasmid were collected from 49 plant species during nocturnal surveys in the forest understorey. In most cases (35 plant species), experiments confirmed that these phasmids fed on those plant species from which they were collected. Partitioning of phasmid species among food plant species was highly significant. Two common species had a largely restricted diet: Asceles margaritatus occurred mainly on Mallotus spp. (Euphorbiaceae) and Dinophasma ruficornis on Leea indica (Leeaceae). Other phasmids fed on a broad spectrum of plant families and can be considered polyphagous (e.g. Haaniella echinata, Lonchodes hosei herberti). Feeding experiments were performed on captive phasmids using leaves from eight plant species. Asceles margaritatus showed a significantly higher consumption rate for Mallotus miquelianus leaves than for other plants, while H. echinata showed the opposite trend and the lowest consumption for M. miquelianus. However, A. margaritatus readily accepted foliage from several plant families, particularly when Mallotus was not offered at the same time. Therefore, studies on host specialisation by herbivores need to include their distribution in the natural vegetation.