Technical Abstract: Thermotolerance of codling moth, Cydia pomonella (L.) (Lepidoptera: Tortricidae), and navel orangeworm, Amyelois transitella (Walker) (Lepidoptera: Pyralidae), were studied using two water immersion methods and one dry heat method. The two water immersion methods were: 1) directly immersing in hot water with insects held in fully exposed screen tubes (direct immersion method) and 2) immersing in hot water solid copper tubes containing insects submerged in tap water (tube immersion method). The dry heating method involved heating insects in computer-controlled heating blocks (heating block system, or HBS). Each test insect was treated at three temperature-time combinations and exposures were adjusted so that each method received the same equivalent accumulated lethal time. In five of the six tests, the HBS provided the lowest mean insect mortality among the three methods, although no significant differences were observed between the direct immersion and the HBS methods. The mean insect mortality obtained with the tube immersion method was significantly higher than that from the direct immersion method and the HBS in four and three of the six temperature-time combinations, respectively. When compared with the two water immersion methods, the HBS method yielded lower mortality data with less variation, resulting in more conservative treatment recommendations.