The potato tuber worm, Phthorimaea opeculella Zeller, is an important worldwide insect pest of solanaceous crops. The tuber resistance mechanism of two potato cultivars, Allegany and Q-174-2, was evaluated by measurement of larval establishment, larval/pupal weight and duration of development. These parameters were examined using intact periderm vs. peeled tubers, sprouts vs. lenticels and intact periderm vs. harvest cracks. Larval establishment and weight on Allegany were significantly greater as compared to Q-174-2. The presence of tuber periderm decreased larval establishment on both cultivars. However removal of periderm did not reduce significant larval establishment difference between Allegany and Q-174-2. Larval survival was the greatest when neonates were given tubers without periderm. When neonates were confined to sprouts, harvest cracks, lenticels and normal periderm, survival was greatest on sprouts, followed by harvest cracks. The greatest larval mortality was observed when neonates were forced to feed through normal periderm. The results indicated that Q-174-2 has significant level of antibiosis to potato tuber worm.