Mortality ofDendroctonus simplexLeConte was investigated near St. John's, Newfoundland, in 1983, where two broods were produced. The fourth larval instar had the highest mortality at 18.9% and pupae the lowest at 2.9%. Percent mortality of the third and fourth larval instars was significantly less in the lower meter of the bole than at 2.5–3.5 m and 5.0–6.0 m above ground. Egg mortality within the second brood was 69% higher than within the first brood. Total mortality was 79% and 82% for first and second broods, respectively. Generally, pathogens caused the highest mortality among eggs, second-instar larvae, and pupae; resinosis among first-instar larvae; and parasitoids among third- and fourth-instar larvae. Prewinter mortality among new brood adults was 6.4% and 8.7% for the first and second broods, respectively.