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The Asian gypsy moth, Lymantria dispar , as one of the most important forest pests in the world, can feed on more than 500 species of host plants, causing serious damage to the forests. Poplar is one of the favorite host plants of L. dispar. The present study aimed to explore the effects of poplar secondary metabolites on the growth and detoxification function of L. dispar larvae. We also aimed to study the expression of glutathione S-transferase (GST) genes in different developmental stages and in response to treatment with secondary metabolites. Six kinds of main secondary metabolites and three groups of characteristic mixed secondary metabolites were selected as follows: Caffeic acid, salicin, rutin, quercetin, catechol, flavone, mixture 1 (salicin and flavone), mixture 2 (salicin, caffeic acid and catechol), and mixture 3 (flavone, caffeic acid and catechol) according to the content changes of secondary metabolites in poplar. The thirteen GST genes were selected as candidate genes to study the expression of GST genes in different developmental stages and after treatment with secondary metabolites using quantitative real-time reverse transcription PCR. The LdGSTe4 and LdGSTo1 genes could be induced by secondary metabolites and were screened to explore their detoxification function against secondary metabolites using RNA interference technology. The results showed that salicin and rutin significantly induced the expression of LdGSTe4 and LdGSTo1. Under the stress of secondary metabolites, LdGSTe4 silencing affected the adaptability of L. dispar larvae to salicin and rutin. LdGSTe4 silencing resulted in a significant decrease in the body weight of L. dispar , but had little effect on the relative growth rate, relative consumption rate, efficiency of conversion of ingested food, efficiency of conversion of digested food, and approximate digestibility, as well as the survival rate and development time. These results provide a deeper understanding of the adaptive mechanism of L. dispar to host plants, form the foundation for the further research into the host resistance mechanism, and identify target genes for breeding resistant transgenic poplar. Thirteen GST family genes were identified from the transcriptome of gypsy moth by bioinformatics analysis. After feeding with six main poplar secondary metabolites, the changes of GSTs gene expression level contribute to the defense function of gypsy moth. Among them, salicin and rutin significantly induced the expressions of LdGSTe4 and LdGSTo1 genes. Under the stress of secondary metabolites, LdGSTe4 silencing affected the adaptability of L. dispar larvae to salicin and rutin. [Display omitted] • Thirteen GST genes were identified from the Asian gypsy moth, Lymantria dispar. • The developmental expression of GST genes was studied. • GST expressions in response to poplar secondary metabolites were studied. • Larval LdGSTe4 and LdGSTo1 expression was induced by salicin and rutin stresses. • LdGSTe4 silencing affected the adaptability of L. dispar larvae to salicin and rutin. [ABSTRACT FROM AUTHOR]