Transgenic overexpression of P450 genes confers deltamethrin resistance in the fall armyworm, Spodoptera frugiperda

The fall armyworm (FAW), Spodoptera frugiperda, is a polyphagous insect pest feeding on many host plants, including some major crops such as corn and rice. This pest has also developed resistance to many insecticides. Recent genome and transcriptome sequencing efforts identified 117-425 P450 genes in the FAW, but their function in detoxifying plant toxins and insecticides is largely unknown. This study found that a P450 gene, SfCYP321A8, is upregulated in the first instar FAW larvae fed on deltamethrin. A transgenic FAW overexpressing SfCYP321A8 was produced to investigate its function in deltamethrin resistance. Transgenic FAW expressing the gene coding for a P450 known to metabolize deltamethrin in Tribolium castaneum, TcCYP6BQ9, was also produced. P450 genes are highly expressed in different tissues of transgenic larvae. The P450 activity in the midgut and fat body of both transgenic FAW lines is significantly higher than in wild-type larvae. Deltamethrin bioassays showed that the transgenic larvae expressing SfCYP321A8 or TcCYP6BQ9 are 10.3- or 15.3-fold more tolerant, respectively, than the wild-type larvae. These studies report on the production of FAW transgenic lines expressing P450 genes and show that SfCYP321A8 contributes to deltamethrin resistance in FAW. The transformation methods developed could be used in functional genomics studies in FAW and other lepidopteran pests.