Mean development times at the chamber level for eggs, larvae, and pupae of the armyworm,Pseudaletia unipuncta(Haworth), were determined under daily temperature reigmes which yielded the same degree-day (DD) accumulation per day, but differed in the amplitude of temperature variation. Regimes with 0, 6.5, and 13°C amplitudes were tested at 9 and 14 DD/d accumulation rates. For each treatment combination, mortality and the distribution of development times were also determined. In general, all life stages developed more quickly under higher amplitude regimes. A nonlinear model predicted this developmental acceleration for some life stages under low accumulation rate regimes, but incorrectly predicted effects of amplitude under high accumulation rate regimes. Nonlinear development rates with respect to temperature and decreased high temperature inhibition were indicated. Other inexplicable effects were observed. Additional instars occurred in some insects descended from a Maryland collection, but never in insects descended from New York collections. Protogyny was observed.