Constant temperatures from 12.5 to 37.5°C influenced duration of the within-tree life cycle (egg to adult emergence) ofIps calligraphus(Germar). The relationship of median development time and constant temperature formed a backwards J-shaped curve. On the average, developingI. calligraphusspent as little as 18 d in the host at 35°C and as much as 224 d in the host at 12.5°C. Frequency distributions of development times changed with temperature and were nearly uniform at 15°C, more symmetric at 20–3O°C, and somewhat skewed to the right at 32 and 35°C. The model of Sharpe&DeMichele (1977, J. Theor. Biol. 64: 649–670) described development rates (reciprocal of median times) as a function of temperature (R2= 0.999), and a cumulative Weibull function (Wagner et al. [1984b, Ann. Entomol. Soc. Am. 77: 475–487]) described a single, temperature-independent distribution of normalized development times (R2= 0.997). Combined, these functions predicted cumulative proportions of cohort emergence through time. Models were validated using a multiple-cohort simulation procedure (Wagner et al. [1985b, Ann. Entomol. Soc. Am. 78: 691–704]) as well as data onI. calligraphusemergence from three trees in each of three field plots. The validation suggested the model's suitability in a larger model of population dynamics.