This study aims to investigate the changes in digestive and detoxification enzyme activities, growth and development, and nutritional effects in the 4th-6th instar larvae of Hyphantria cunea after feeding on various host trees. It also seeks to analyze the adaptation mechanisms of H. cunea to different host trees.

The 4th-6th instar larvae were raised indoors on the leaves of Ulmus pumila, Juglans mandshurica, Tilia amurensis, Salix matsudana, Betula platyphylla, and Albizia kalkora. The correlation between the activities of digestive enzymes (α-amylase, lipase, trypsin) and detoxification enzymes (glutathione-S-transferase (GSTs), acetylcholinesterase (AchE), carboxylesterase (CarE)) and their growth, development, and nutritional effects were analyzed.

1) As the instar stage increased, the midgut α-amylase activity significantly decreased, while lipase activity significantly increased. Trypsin activity initially decreased and then increased. GSTs and AchE activities decreased, with a notable decline in AchE, whereas CarE activity first decreased and then increased; 2) No significant correlation was observed between midgut α-amylase activity in the 4th-6th instar larvae and GSTs activity in the 5th-6th instar larvae. However, GSTs activity in the 4th instar larvae showed a significant correlation with growth and development indicators, except for food intake; 3) Except for α-amylase and GSTs, the activities of other enzymes in the 4th-5th instar larvae were significantly positively correlated with body weight, body length, head width, food intake, food utilization rate, and conversion rate, but negatively correlated with food consumption rate; 4) In the 6th instar larvae, growth and development indicators were only significantly correlated with CarE activity, with body length, food utilization efficiency, and conversion rate being positively correlated, and food consumption rate being negatively correlated.

The enzyme activity of H. cunea larvae varied after feeding on six host trees. By regulating enzyme activity, H. cunea larvae can control nutrient absorption and utilization, allowing for normal growth and development. This regulation also enhances their adaptability to different host trees and expands their host range.