[Aim]  To clarify the insecticidal activity, and combined efficacy, of four biotic pesticides, chlorbenzuron, tebufenozide, matrine, and azadirachtin, on Hyphantria cunea larvae. [Methods]  The toxicity of four pesticides, both when applied separately and as a mixture, on the 4th instar larvae of H. cunea was determined using a surface contamination bioassay and an artificial diet. First, the co-toxicity factor method was used to identify the combination with the best synergistic effect, after which the co-toxicity coefficient method was used to identify the optimal mixing ratio. [Results]  The relative toxicity of the four biotic pesticides was azadirachtin > chlorbenzuron > matrine > tebufenozide. The median lethal concentration (LC₅₀) 96 h after application was 1.732, 23.702, 30.160, and 54.296 mg·L^-1, respectively. A mixture of chlorbenzuron and tebufenozide had significant synergistic effects at lethal concentrations, and this was most significant at a ratio of 9∶1, with a co-toxicity coefficient of 278.462. The median lethal time (LT₅₀) of this combination was 0.704 and 1.281 d less, respectively, than that for tebufenozide or chlorbenzuron. Other pesticide mixtures displayed antagonistic or additive effects. [Conclusion] The four biotic pesticides tested have high insecticidal activity against 4th instar H. cunea larvae, but only a mixture of chlorbenzuron and tebufenozide had significant synergistic effects. The best results were achieved at concentrations of chlorbenzuron and tebufenozide of 23.702 and 54.296 mg·L^-1, respectively, and at a volume ratio of 9∶1.