Objective This paper aims to explore the adaptive mechanisms of Endoclita vietnamensis larvae to different host plants with varied degrees of preference, clarify the co-evolutionary relationship between herbivorous insects and their host plants, and provide a theoretical basis for biological control of this pest.

Method Three host plants with different levels of palatability, i.e. Eucalyptus grandis × E. urophylla (high palatability), Mallotus apelta (medium palatability), and Broussonetia papyrifera (no palatability) were selected as study subjects. The physical and chemical properties of the host plants and physiological responses of the larvae after feeding were measured. Larval feeding rates and survival rates were statistically analyzed, and potential correlations among the indicators were explored through correlation analysis.

Result (1) The analysis of physical and chemical properties of host plants showed that the content of reducing sugar and soluble sugar in the bark was key factor affecting host selection of the larvae, and the content was in the order of E. grandis × E. urophylla > M. apelta > B. papyrifera, which was completely consistent with the order of larval preference. (2) Flavonoids, as the core defense substances of host plants, were significantly induced to accumulate after larval feeding, but their contents were significantly positively correlated with larval feeding rates, indicating that the larvae had developed an effective tolerance mechanism. (3) Larvae dynamically regulated their enzymatic systems to adapt to a multi-host environment: protective enzymes (SOD, CAT) were continuously activated, detoxification enzymes (AchE, GST) reached their peak in the middle of feeding, and protease activity was significantly down-regulated. (4) Correlation analysis confirmed that the larval feeding rate was significantly positively correlated with the content of reducing sugar in host bark, and significantly positively correlated with the content of soluble sugar, flavonoids, and the activity of AchE in larvae themselves.

Conclusion The larvae of E. vietnamensis adapt to multiple hosts by perceiving sugar signals from the hosts and dynamically regulating the enzyme system. This study provides a theoretical basis for understanding the co-evolution of insects and plants and the biological control of pests.