Knockdown of the β-N-acetylhexosaminidase genes by RNA interference inhibited the molting and increased the mortality of the white-backed planthopper, Sogatella furcifera.

β-N-Acetylglucosaminidases and/or β-N-acetylhexosaminidases (NAGs / Hexes) are crucial exonucleases, playing a crucial role in the insect molting process. SfHex3 and SfHex4 contain conserved catalytic domains of GH20 and GH20b, clustered into NAG2 and NAG1 group, respectively. SfHex3 and SfHex4 were mainly highly expressed in the 4th-5th instar nymphs, as well as in the integument and ovary. The expression level of SfHex3 gradually decreased in male and female adults, and SfHex4 on the first day of female was significantly higher than that on the first day of male. In addition, RNA interference (RNAi) results demonstrated that the downregulation of SfHex3 and SfHex4 expression in 5th-instar nymphs resulted in failed molting, and a high mortality. Furthermore, after RNAi with SfHex3 and SfHex4, the transcript levels on key genes of the chitin metabolism pathway (SfCHS1, SfCHS1a, SfCHS1b, SfTRE1, SfTRE2, SfCht5, and SfCht7) were significantly decreased compared to the control group. Meanwhile the expression levels of SfHex3 and SfHex4 were up-regulated after 6 h and 12 h of 20E treatment. And the transcription levels of SfHex3 and SfHex4 were significantly inhibited at nitenpyram LC ₂₀ , LC ₅₀ , and LC ₉₀ after 96 h of treatment, in 3rd nymphs of Sogatella furcifera. In conclusion, SfHex3 and SfHex4 play important roles in the nymphal development of S. furcifera, contributing to the molting process from nymph to adult. This study not only enhances our understanding of the nitenpyram in pest control, but also provides a foundation for the development of new control strategies using RNAi to targeting SfHex3 and SfHex4.
Competing Interests: Declaration of competing interest The authors declare no conflict of interest. The authors alone are responsible for the content and writing of the paper.
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