Eggs of western corn rootworm,Diabrotica virgiferaLeConte, in different embryonic stages separated according to their sp. gr. were exposed to 4 temperatures and their viability was determined. Results indicated that, in developing eggs, survival was adversely affected by a chill period of 12 wk. The effect was more pronounced at more advanced stages of development and at lower chill temperatures. Overall % hatch means for 20°, 10°, 5°, and 0°C were 81.7, 63.3, 45.7, and 31.0, respectively. Results also showed that time to hatch was delayed and the duration of hatching was shortened following chill. Thus, if eggs developed in the field during the fall they would not survive and hatch in the spring, and the species would not adapt to produce 2 generations per season.