[Aim]  To investigate whether the ingestion of fumonisin B₁ in maize tissues by Helicoverpa armigera could contribute to the increase in resistance of this pest to λ-cyhalothrin. [Methods]  Fumonisin B₁ was added to the feed of H. armigera and its effect on the resistance of H. armigera to λ-cyhalothrin was determined. Key detoxification genes were identified by transcriptome sequencing and RNAi technology, and the effects of fumonisin B₁ and λ-cyhalothrin on the expression of these genes was verified with RT-qPCR. [Results]  After feeding on a diet containing 0.01 and 0.1 mg/kg of fumonisin B₁, the LC₅₀ values of H. armigera to λ-cyhalothrin were 1.31 and 1.43 times higher, respectively, than those of the control group. The key detoxification gene HaCYP6AE19 was identified by transcriptome sequencing. After silencing this gene, the LC₅₀ value of H. armigera to λ-cyhalothrin was 2.59 times that of the control group. There was no significant change in HaCYP6AE19 expression after 1 day (P>0.05) of either fumonisin B₁ or λ-cyhalothrin stress. However, after 2 days the expression of this gene in the fumonisin B₁ and λ-cyhalothrin treatment groups was 4.44 (P<0.01) and 2.39 (P<0.05) times, respectively, that of the control, and after 3 days, its expression was 5.27 (P<0.01) and 6.25 (P<0.01) times, respectively, that of the control. [Conclusion]  Ingestion of fumonisin B₁ by H. armigera causes overexpression of the detoxification gene HaCYP6AE19 and thereby enhances resistance to λ-cyhalothrin.