The potato tuberworm (PTW) Phthorimaea operculella Zeller is an important pest of solanaceous crops including potato Solanum tuberosum L. Overwintering of the pest in the Columbia Basin of Oregon and Washington is an extreme case of its survival as PTW is a pest in tropical and subtropical regions. The various PTW life stages were studied to determine whether overwintering adaptation occurred. In early January 2007, eggs and tubers infested with 1st instar larvae and pupae, were buried in the soil at depths of 0, 6, 10 and 20 cm. Each PTW life stage was approximately weekly removed from the soil and survival was estimated. The eggs were able to survive up to 54 d with the greatest survival observed at 6 cm soil depth and the lowest survival at 0 cm soil depth. However, egg survival was significantly reduced after one month of exposure to winter conditions. Larvae were able to survive up to 30 d with the greatest survival observed at 20 cm soil depth. All infested tubers kept at 0 and 6 cm soil depth were killed by frost. Compared to eggs and larvae, the pupae showed the greatest tolerance to winter temperature. Pupae were able to survive up to 90 d of exposure to winter temperatures averaging 0, 4 and 9 ºC during January, February and March respectively. Initial results suggested that PTW would not be able to overwinter as eggs or larvae but could overwinter as pupae in the Columbia Basin. Additional studies are needed to determine the overwintering mechanism of PTW in the Columbia Basin.