Feeding Preferences of Phasmids (Insecta: Phasmida) in a Bornean Dipterocarp Forest.

Stick and leaf insects (Phasmida) from 19 species (53 individuals) were collected in a lowland dipterocarp forest (Lambir Hills, Sarawak, Malaysia).  Dual-choice tests were conducted to examine whether phasmids discriminate between young and old leaves of seven plant species.  A second set of tests examined the preferences of phasmids for leaves from Dryobalanops lanceolata (Dipterocarpaceae) saplings versus leaves from the upper canopy of the same tree species.  Haaniella echinata and other flightless species (Heteropterygidae and Lonchodinae) fed on nearly all plant species offered and showed significant preferences for old leaves in three plant species.  In contrast, flying phasmids (Ashiphasmatinae and Necrosciinae) rejected leaves from most plants and did not show consistent leaf age choices.  H. echinata and flightless phasmids preferred canopy leaves from D. lanceolata over leaves from saplings, regardless of leaf age.  Our results are consistent with the hypothesis that young leaves of some plant species are better defended against generalist herbivores than old leaves and that saplings are better defended than adult trees.  Since upper canopy leaves were highly palatable to understorey phasmids, factors other than chemical defences must contribute to the low abundance of phasmids in forest canopies.