Abstract: 【Aim】 This study aims to clarify the effects of host switch on the development and digestive enzyme activities of the larvae of the fall webworm, Hyphantria cunea, and to further explain the adaptive and physiological response mechanisms of H. cunea larvae after switching between different host plants.【Methods】 Under laboratory conditions, the first generation of H. cunea was reared on artificial diets. Following that the newly hatched larvae of H. cunea of the second generation were continuously reared on Taxodium distichum (T-T population) and Cerasus serrulata (C-C population), respectively. Then the larvae of H. cunea reached the 3rd instar, T-T and C-C populations were fed with their original and switched host plants, respectively, resulting in four treatment combinations: T-T population, C-C population, H. cunea population feeding on C. serrulata switching from feeding on T. distichum (T-C population), and H. cunea population feeding on T. distichum switching from feeding on C. serrulata (C-T population). Meanwhile, the growth and development parameters (developmental duration, larval survival rate, mean larval weight and pupal weight) of H. cunea larvae and the nutrition indices ［relative growth rate (RGR), relative consumption rate (RCR), efficiency conversion of ingested food (ECI), efficiency conversion of digested food (ECD) and approximate digestibility (AD)］ of the 5th instar larvae of the four treatments were tested. Furthermore, the activities of six digestive enzymes ［total protease, high-alkaline trypsin, low-alkaline trypsin, chymotrypsin, amylase, and lipase］ in the midgut of the 4th instar larvae of H. cunea during host switching were examined by the enzyme kinetics method. 【Results】 Under the conditions of host switch, there were significant differences in the developmental duration, pupal weight, and larval survival rate of H. cunea. The T-T population had the shortest larval and pupal duration and the highest larval survival rate, while the C-C population had the longest larval and pupal duration and the highest larval mortality rate. Meanwhile, there were significantly different growth and development indices of H. cunea larvae from earlier hosts after switching hosts. The RCR of the T-C population of H. cunea larvae was significantly lower than those of the other populations, and the ECI and ECD of the T-C population were significantly higher than those of the other populations. The AD of the T-C population was the lowest, while that of the C-C population was the highest.There was no significant difference in AD betweem the other two populations. After the host switching treatment, the digestive enzymes in the midgut of H. cunea larvae showed different activity levels. The trypsin activity in the larval midgut of the C-C population was significantly higher than those of the other populations, the chymotrypsin activity in the larval midgut of the C-C population was significantly higher than those of the T-T and T-C populations, the amylase activities in the larval migdut of the C-C and C-T populations were significantly higher than those of the other populations, and the lipase activity in the larval midgut of the T-C population was significantly lower than those of the other populations. 【Conclusion】 The growth, development, and digestive enzyme activities of H. cunea larvae have shown different degrees of differences after host switch. This study clarified the phenotypic plasticity and digestive physiological response of H. cumea after host switch. The results provide a foundation for revealing the adaptations of H. cunea to host plants and the mechanisms of plantmediated expansion into disaster risk.

Key words: Hyphantria cunea, host switch, growth and development, digestive enzyme, nutritional effect