Development time forPlagithmysus bilineatusSharp was studied on the northeast slope of Mauna Loa, on the island of Hawaii. Host substrates (bolts and live stumps) ofMetrosideros polymorpha(Gaudichaud) were monitored at four sites 305, 915, 1,274, and 1,707 m high. Mean development time ranged from 160 to 380 d and was significantly influenced by temperature, site, and host substrate. Longer development time was associated with lower temperatures, sites at higher elevations, and live host tissue. The estimating equation that included parameters for late instars, the pupal stage, and location explained 91% of the variation for development in bolts with a 95% prediction interval of 75 d. The best estimating equation for development in live stumps explained 76% of the variation, with a 95% prediction interval of 123 d.