Determining thermotolerance of fifth-instar Cydia pomonella (L.) (Lepidoptera: Tortricidae) and Amyelois transitella (Walker) (Lepidoptera: Pyralidae) by three different methods S. Wang a , J.A. Johnson b , J.D. Hansen c , J. Tang a, * a Department of Biological Systems Engineering, Washington State University, 213 L. J. Smith Hall, Pullman, WA 99164-6120, USA b USDA-ARS San Joaquin Valley Agricultural Sciences Center, 9611 S. Riverbend Avenue, Parlier, CA 93648, USA c USDA-ARS Yakima Agricultural Research Laboratory, 5230 Konnowac Pass Road, Wapato, WA 98951, USA article info Article history: Accepted 11 January 2009 Keywords: Cydia pomonella Amyelois transitella Heating block Quarantine Thermal mortality abstract Thermotolerances of codling moth, Cydia pomonella (L.) (Lepidoptera: Tortricidae), and navel orange- worm, Amyelois transitella (Walker) (Lepidoptera: Pyralidae), were determined using two water- immersion methods and one dry-heat method. The two water-immersion methods were: 1) directly immersing screen tubes containing test insects in hot water (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 statistically 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 tempera- ture-time combinations, respectively. When compared with the two water-immersion methods, the HBS method yielded lower mortality data with less variation at the same mortality level, resulting in more conservative treatment recommendations. Ó 2009 Elsevier Ltd. All rights reserved. 1. Introduction To develop effective thermal treatments against insect pests, it is essential to determine the most heat resistant species and their life stages by experimenting with an appropriate heating method in vitro (Tang et al., 2000; Wang et al., 2002c). The experimental method should simulate the real heating environment for the infested insects in targeted agricultural commodities (Thomas and Shellie, 2000). Important factors that influence insect mortality in the experiments are treatment substrate, humidity, oxygen level, heating uniformity, heating rate, final temperature, and holding time. A reliable experimental method should provide a precise and controlled temperature profile for the whole pop- ulation of test insects, in order to avoid the confounding effects of slow heat transfer and inconsistent heating experienced by each insect during the heating period (Jones and Waddell, 1997; Lurie et al., 2004). Insect mortality data vary with heating methods, handling processes and specific test conditions. Therefore, it is important to identify the test method most appropriate for the generation of mortality data used in developing large-scale treatments. Several methods are commonly applied for studying thermo- tolerance of insects in vitro. One method directly exposes insects in a water bath for specific times (Sharp and Chew, 1987; Jones and Waddell, 1997; Waddell et al., 2000). Another places insects in tubes which in turn are submerged in water baths (Yokoyama et al., 1991; Thomas and Mangan, 1997; Follett and Sanxter, 2001; Lurie et al., 2004). Neven (2008) developed a glass tube immersion system for assessment of insect mortality under combination heat and controlled atmosphere treatments. Hansen and Sharp (1998) hypothesized that the direct water-immersion method restricts oxygen supply to the heated larvae and thus leads to higher thermal mortality data than the methods that provide an adequate supply of air. This has been demonstrated with codling moth larvae, Cydia pomonella (L.) (Lepidoptera: Tortricidae) (Hansen and * Corresponding author. Tel.: þ1 509 3352140; fax: þ1 509 3352722. E-mail address: jtang@wsu.edu (J. Tang). Contents lists available at ScienceDirect Journal of Stored Products Research journal homepage: www.elsevier.com/locate/jspr 0022-474X/$ – see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.jspr.2009.01.001 Journal of Stored Products Research 45 (2009) 184–189