Soil temperatures were monitored at two depths in the plow layer during the prediapause and diapause-chill quiescent stages of the western corn rootworm,Diabrotica Virgifera virgiferaLeConte, for four years at Brookings, SD. Soil tempratures descended below the threshold for development (11°C) in early October and remamed<0°C until early March. Each year, eggs at both depths were subjected to a minimum of 14 weeks at temperatures<0°C. In laboratory tests, hatch declined significantly with time at −7.5°C and −10°C.