Abstract: 【Aim】 The aim of this study is to clarify whether the experience of host switch will alter the effects of sublethal concentrations of insecticides on the growth, development and reproduction of Cnaphalocrocis medinalis, so as to provide a theoretical basis for the rational use of insecticides and the integrated management of C. medinalis. 【Methods】 Eggs were collected from the rice and wheat populations of C. medinalis, and transferred to other host plants for feeding until the 2nd instar, as larvae with different experience of host switch ［rice population feeding on rice (R-R), rice population feeding on wheat (R-W), wheat population feeding on wheat (W-W), and wheat population feeding on rice (W-R)］. At 48 h after treatment of these larvae with the sublethal concentration (LC₂₅) of abamectin and chlorpyrifos on rice or wheat leaves using the in vitro leaf impregnation method, the growth and development of the 3rd-5th instar larvae, the reproductive ability and longevity of adults were determined. 【Results】 Without insecticide treatment, host switching significantly affected the total duration of the 3rd-5th instar larvae, pupation rate, and pupal weight of C. medinalis, but had opposite effects on the rice and wheat populations. Treatments with the LC₂₅ of abamectin and chlorpyrifos to the 2nd instar larvae significantly prolonged the total duration of the 3rd-5th instar larvae, but the degree of extension varied depending on the experience of host switch. LC₂₅ of abamectin significantly reduced the pupation rate of larvae undergoing different host switches (except for the R-R group). LC₂₅ of chlorpyrifos only significantly reduced the pupation rate of the W-W group. The pupal weight of the W-W and W-R groups significantly decreased after exposure of the 2nd instar larvae to LC₂₅ of abamectin. The effects of host switching on the pupation rate and pupal weight of rice populations disappeared after treatment with LC₂₅ of abamectin, while the effects of host switching on the pupation rate and pupal weight of wheat populations disappeared after treatment with LC₂₅ of abamectin and chlorpyrifos. No matter which host switch experience or treatments with LC₂₅ of abamectin and chlorpyrifos were used, the adult emergence rate, adult mating rate, and number of eggs laid per female were not affected. Host switching only significantly affected the egg hatching rate of the rice populations without insecticide treatment, but the egg hatching rate was not affected by treatments with LC₂₅ of abamectin and chlorpyrifos. Compared with non-subjected to insecticide treatment, treatments with LC₂₅ of abamectin and chlorpyrifos did not affect the female adult longevity, but treatment with LC₂₅of chlorpyrifos significantly increased the male adult longevity in the W-W group. 【Conclusion】 The experience of host switch can affect the sublethal effects of abamectin and chlorpyrifos on C. medinalis. After treatment with LC₂₅ of abamectin and chlorpyrifos on C. medinalis larvae with the experience of host switch, the growth and development of larvae and pupae were affected to varying degrees, but the effects on adult reproduction and longevity were relatively small. When using insecticides targeting C. medinalis and conducting toxicological experiments, the potential impact of host plant should be considered.

Key words: Cnaphalocrocis medinalis, host switch, abamectin, chlorpyrifos, growth and development, reproduction