Determining thermotolerance of fifth-instar Cydia pomonella (L.) (Lepidoptera: Tortricidae) and Amyelois transitella (Walker) (Lepidoptera: Pyralidae) by three different methods

Authors: WANG, SHAOJIN - WSU; Johnson, Judy; HANSEN, JAMES - RETIRED ARS RES SCIENTIST; TANG, JUMING - WSU

Submitted to: Journal of Stored Products Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/11/2009
Publication Date: 6/2/2009
Citation: Wang, S., Johnson, J.A., Hansen, J.D., Tang, J. 2009. Determining thermotolerance of fifth-instar Cydia pomonella (L.) (Lepidoptera: Tortricidae) and Amyelois transitella (Walker) (Lepidoptera: Pyralidae) by three different methods. Journal of Stored Products Research. 45(3):184-189.

Interpretive Summary: To develop effective heat treatments against insect pests, the most heat resistant life stages must be determined by a heating method that simulates the real heating environment for target insects. Because insect mortality data vary with heating methods, handling processes and specific test conditions, it is important to identify the test method most appropriate for generation of mortality data used in developing large-scale treatments. Heat tolerance of codling moth and navel orangeworm, common insect pests of tree fruit and nuts, were studied using two hot water immersion methods and one dry heat method. The two water immersion methods were: 1) directly immersing in hot water 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 species was treated at three temperature-time combinations and exposures were adjusted so that insects treated by each method received the same exposure to heat. In five of the six tests, the HBS provided the lowest 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. This was due to differences in heating uniformity between the methods. When compared with the two water immersion methods, the HBS method yielded lower mortality data with less variation, resulting in more conservative treatment recommendations, and is recommended for developing rapid heat treatments.

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.