Thermal resistance of fifth-instar Cydia pomonella (L.) (Lepidoptera: Tortricidae) as affected by pretreatment conditioning

Codling moth (Cydia pomonella (L.)) is targeted for postharvest control by quarantine regulations in Japan and South Korea and by phytosanitation concerns in Europe. Heat treatments may be used to control C. pomonella. But possible increase of heat resistance in insect pests, caused by pretreatment thermal conditions during harvest and storage periods, may compromise the efficacy of subsequent thermal treatments. A heating block system was used to determine the effect of pretreatment conditioning on the thermal resistance of the fifth-instar C. pomonella. Results showed that pretreatment conditioning at 35 °C for 40, 120, 360 or 1080 min significantly increased the thermal resistance of C. pomonella. Among the above conditions 35 °C for 360 min resulted in the highest heat resistance for fifth-instars. The minimum treatment times required to reach 100% mortality for 300 larvae that went through thermal conditioning at 35 °C for 360 min were 30, 7 and 3 min at 48, 50 and 52 °C, respectively, as compared with 15, 5 and 2 min at those temperatures without pretreatment conditioning. After a pretreatment at 35 °C for 360 min followed by a period of at least 120 min at 22 °C, fifth-instar thermal resistance returned to the level that had existed before pretreatment conditioning.