The koa moth, Scotorythra paludicola, is an endemic Hawaiian moth that undergoes sporadic outbreaks in koa forests in Hawai‘i, causing vast defoliations of its host plant, Acacia koa. We studied one such outbreak that occurred on East Maui in 2003, in which approximately 16 km² of forest were defoliated. We collected adult moths and larvae, and recorded size-class distribution of larvae in defoliated regions. Larvae at a given site tended to be of a similar size class, suggesting that outbreaks were synchronous, and mean development time from first instar to adulthood was 42 days under laboratory conditions. Mortality of field-collected, laboratory-reared larvae due to disease was high (80%), making it impossible to quantify meaningful parasitism rates, but three nonnative hymenopteran primary parasitoids were reared (the braconids Meteorus laphygmae and Cotesia marginiventris, and the ichneumonid Hyposoter exiguae). One ichneumonid hyperparasitoid, Gelis sp., was also reared. No native parasitoids were reared. We found no relationship between occurrence of five koa moth outbreaks on East Maui between 1920 and 2006 and annual or monthly precipitation or temperature during that period.