Caterpillar assemblages on Chusquea bamboos in southern Ecuador: abundance, guild structure, and the influence of host plant quality

1. Information on the guild structure of foliage-associated tropical insects is scarce, especially as caterpillars are mostly considered only as herbivores feeding on living leaves. However, many caterpillar species display alternative trophic associations, feeding on dead or withered leaves or epiphylls ('non-herbivores'). 2. To determine the contribution of these non-herbivores, caterpillar communities associated with Chusquea Kunth (Poaceae) in the Andes of southern Ecuador were investigated. Caterpillars were collected at two elevation levels (montane rainforest similar to 2000 m and elfin forest at similar to 3000 m a.s.l.) and assigned to three feeding guilds (strict herbivores, non-herbivores, and switchers) based on feeding trials. Foliage quality and leaf area were recorded to test for their influence on guild composition and caterpillar density. 3. Three hundred and eighty-nine individuals belonging to 175 Lepidoptera species associated with Chusquea bamboos were found. The species richness of caterpillars was similarly high at both elevation levels but varied between feeding guilds. Approximately half (46.5%) displayed an alternative feeding association, i.e. were non-herbivores (31.1%) or switchers (15.4%). 4. Caterpillar density was nearly two-fold higher in the elfin forest, but only strict herbivores and switchers increased significantly with elevation. Leaf area positively influenced the density of strict herbivores and switchers; foliage quality only affected strict herbivores. The density of non-herbivores did not differ significantly between the forest types and was not related to leaf area or foliage quality. 5. The present study underpins that non-herbivores make up a considerable fraction of caterpillar communities in tropical mountain ecosystems and demonstrates that elevation, foliage quality and available plant biomass further shape feeding guild composition.