Lepidopteran insect species-specific, broad-spectrum, and systemic RNA interference by spraying dsRNA on larvae

TLDR: Results provide direct evidence confirming that dsRNA is a biologically safe insecticide in lepidopteran insect pest control and confirmed that 21 nucleotide siRNAs are unlikely to produce the off‐target effect if conserved genes are not selected.

Abstract: To investigate whether the dsRNA of a gene has species-specific, broad-spectrum, or off-target effects on lepidopteran insects, we identified a methionine-rich storage protein gene (OfSP) from Asian corn borer, Ostrinia furnacalis (Guenee) (Lepidoptera: Pyralidae), using high-throughput sequence technology. The OfSP gene possesses three functional domains (N, M, and C), which are predominantly expressed in the last instars of Asian corn borer. This gene is also a key element for insect development and reproduction. The dsRNAs for the three functional domains of the OfSP gene were synthesized and sprayed on either Asian corn borer or on cotton bollworm, Helicoverpa armigera (Hubner) (Lepidoptera: Noctuidae), during the first instar. The dsRNA targeting the C-terminal domain can cause high mortality rates in both insects, whereas those targeting the M- and N-terminal domains only cause high mortality in the Asian corn borer. These results can be used to develop dsRNA with species-specific or broad-spectrum bio-insecticidal properties. More importantly, after dsRNA spraying, we also found typical systemic RNAi in the phenotypes that resulted in abnormal ecdysis of the larvae and pupae. Moreover, sterile eggs were found in the next generation. To analyze the broad-spectrum link to dsRNA off-target effects, the whole transcriptome siRNA libraries for these two species were constructed. Results further confirmed that 21 nucleotide siRNAs are unlikely to produce the off-target effect if conserved genes are not selected. These findings provide direct evidence confirming that dsRNA is a biologically safe insecticide in lepidopteran insect pest control.