Abstract: Abstract: 【Aim】 The frequency of insects encountering heat stress is increasing under the situation of global warming. Insects will generate heat acclimation when repeatedly impacted by short-term high temperature. However, the transgenerational effect of heat adaptation induced by acclimation is still not very clear. The rice leaf folder, Cnaphalocrocis medinalis, is a serious pest of rice, and its larvae can adapt to high temperature when they are acclimated to a specific temperature for several generations. This study aims to illustrate the transgenerational heat adaptation of C. medinalis, so as to provide the guidance for the forecast of its population trends under global warming using the index of temperature. 【Methods】 The 1st-5th instar larvae of the heat-acclimated strains HA39 and HA41 of C. medinalis after 30 generations of acclimation to 39℃ and 41℃, respectively, and the unacclimated strain HA27 established in the laboratory were exposed to different high temperatures (36℃ and 41℃) for different time (1-144 h), and then their survival rates were examined and the heat tolerance was assessed. The hybridization experiments between HA39 and HA27 were performed to examine the fecundity of various mating combinations and the heat tolerance of the 3rd instar larvae of their offspring. The heat tolerance of the 3rd instar larvae from HA39 was also measured after stopping heat acclimation for two generations. 【Results】 The short-term heat exposure of C. medinalis at the 3rd instar larval stage for multiple generations increased the heat tolerance of not only the 3rd instar larvae but also the other instar larvae to a specific heat stress. When exposed to 36℃ and 41℃ for a specific duration, the survival rates of larvae of HA39 and HA41 were significantly higher than that of HA27. The heat tolerance of larvae was dependent on the acclimation temperature. Acclimation to 39℃ increased the survival rates of the 4th instar larvae exposed to 36℃ for 2 and 4 d and the 5th instar larvae exposed to 41℃ for 5 and 6 h, but the acclimation to 41℃ could not. The fecundity among the self-bred and crossbred offspring of HA39 and HA27 was not significantly different. The heat tolerance of the crossbred offspring showed that the survival rates of the 3rd instar larvae of the crossbred offspring exposed to 41℃ for 5 and 6 h were comparable to that of the self-bred offspring of HA39, and significantly higher than that of the self-bred offspring of HA27. The heat tolerance acquired by acclimation could be transferred into the offspring from parents. When the heat acclimation to 39℃ had stopped for two generations, the survival rate of the 3rd instar larvae of HA39 exposed to 39℃ for 4 h was significantly higher than that of HA27, but those of HA39 exposed to 39℃ for other time and exposed to 36℃ and 41℃ for 1-7 h showed no significant difference from those of HA27,indicating that the tolerant ability of the heatacclimated strain to high temperature can still be partially maintained in two generations after stopping heat acclimation. 【Conclusion】 The heat adaptation of C. medinalis larvae has the transgenerational effect. The ability of C. medinalis populations to adapt to high temperature is likely increasing under longterm global warming, and therefore the negative effect of high temperature in summer upon its populations will be weaker, and consequently its population outbreaks will be frequent.

Key words:  Cnaphalocrocis medinalis, heat acclimation, high temperature, survival rate, transgenerational effect