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.

The study aims to assess the residual levels and potential ecological risks of heavy metals-Zn, Pb, As, Cr, Cu, Hg, and Cd-in the soil of returned farmland wetlands within the Naolihe national nature reserve. This assessment seeks to provide reference data for wetland restoration and protection efforts within the reserve.

A total of 57 soil samples were collected from Daxing farm, Hongqiling farm, ‘853’ farm, and ‘597’ farm, each representing different reforestation periods within the Naolihe reserve basin. The soil samples were processed using a mixed acid-electrothermal plate digestion method. The study analyzed the differences in residual heavy metals across return plots from 1-year (R1), 2-year (R2), 8-year (R8), 17-year (R17), as well as corn (CF), soybean (SF), rice (RF), and natural wetland (NW) plots. The single factor pollution index (P), geological accumulation index (I_geo), and potential ecological risk index (R_I) were employed to evaluate the potential ecological risk levels of heavy metals in the soil.

The residual concentrations of Zn, Pb, As, Cr, Cu, Hg, and Cd in the Naolihe reserve soil ranged from 0.39-0.98, 0.21-0.35, 0.63-2.85, 1.54-2.34, 1.77-3.88, 0.74-2.24, and 0.12-0.54 mg·kg^-1, respectively. The residual concentrations of Zn, Pb, As, Cr, and Cu were all below the soil background values for the Sanjiang plain, whereas Hg and Cd levels exceeded these background values. The evaluation results using the single factor pollution index indicated that Cu, Cr, Zn, As, and Pb were pollution-free across all locations. Hg pollution was moderate to severe in R1, R2, R8, and farmland plots (CF, SF, RF), while it was mild in R17 and NW plots. Cd showed mild contamination in R1 and farmland plots, with other plots remaining at clean levels. The geological accumulation index evaluation revealed that Cd, Zn, Pb, As, Cr, and Cu were pollution-free in all locations, while Hg exhibited light to moderate pollution. The potential ecological hazard index evaluation indicated that R1, R2, and farmland plots posed medium risks, while R8, R17, and NW plots posed low risks.

The residual levels of heavy metals decreased progressively with longer reforestation periods. After 17 years of reforestation, the residual levels were the lowest and comparable to those in natural wetlands. The ecological risk associated with heavy metal residues in the reclaimed wetland soils of the Naolihe reserve ranged from low to medium. Plots returned to farmland for 8 and 17 years were classified as low-risk. Heavy metals Hg and Cd are the main ecological hazard elements in the returned farmland wetland of the Naolihe reserve.