Hypotheses and lessons from a native moth outbreak in a low‐diversity, tropical rainforest

Abstract Outbreaks of defoliating insects in low‐diversity tropical forests occur infrequently but provide valuable insights about outbreak ecology temperate environments and general. We investigated an extensive the endemic koa moth ( Scotorythra paludicola ), which defoliated trees Acacia ) over a third their range on Hawai‘i Island during 2013 2014. At Hakalau Forest National Wildlife Refuge, we observed dynamics its effects host trees, nutrient cycling, insectivorous consumers reforestation stands densely planted natural forest mixed ‘ōhi‘a Metrosideros polymorpha ). Contrary to predictions resource concentration hypothesis, caterpillar biomass defoliation severity were greater sites, where density was relatively low. Caterpillars preferentially consumed most palatable foliage type (phyllodes), initially refoliated with least (true leaves). Lightly small more quickly than did heavily ones opposite true for large also produced proportion phyllodes. Mortality greatest koa. Caterpillar frass caused larger increases soil nitrogen (N) phosphorus (P) availability, N fine‐textured soils. Foliar increased alien grasses under canopies compared away from native woody understory species. Bird activity influenced by flower abundance defoliation; birds switched outbreaking prey, they gained weight outbreak. Bat foraging times decreased outbreak, apparently because became satiated each night. Parasitoid wasps had little influence dynamics. Reducing grass cover increasing tree diversity would likely reduce impacts insect outbreaks similar perturbations forests.