# The Defensin NldefB as a Potential Target for Brown Planthopper Control Based on the Combination of RNA Interference and Fungal Insect Pathogen

## TL;DR

This study explores how targeting a specific antimicrobial peptide in brown planthoppers can improve biocontrol using RNA interference and fungi.

## Contribution

The study identifies NldefB as a novel target for brown planthopper control through RNAi and microbial integration.

## Key findings

- Silencing NldefB reduced survival, reproduction, and resistance to fungal infection in brown planthoppers.
- NldefB suppression increased microbial load in the insects, suggesting a role in microbial maintenance.
- NldefB expression was highest in female adults and was regulated by pathogen exposure.

## Abstract

The use of pathogenic and symbiotic microbes for pest biocontrol is a promising strategy for achieving sustainable and eco-friendly pest management. However, the robust immune defense system of insects limits the insecticidal efficacy of microbe-based biocontrol. Insect antimicrobial peptides (AMPs) represent a crucial family of potent immune effectors involved in host immune–microbe interaction, yet their potential for pest biocontrol remains largely unexplored. In this study, the gene NldefB which encodes an antimicrobial peptide defensin was identified and functionally characterized in Nilaparvata lugens (brown planthopper, BPH), the most destructive rice pest. RNAi-mediated silencing of NldefB resulted in a marked reduction in survival rate, oviposition amount and hatchability, caused a significant enhancement in susceptibility to fungal infection, and led to a substantial increase in microbial load in BPH. Our findings underscored the critical roles of NldefB in mediating host physiology including reproductive development, pathogen defense, and microbial maintenance, highlighting that NldefB could serve as a target for BPH control by integrating RNAi and pathogenic/symbiotic microbes.

Defensins are a class of small cysteine-rich cationic antimicrobial peptides (AMPs) that play vital roles in immune-regulating insect–microbe interaction, offering great potential for developing pest control approaches using RNA interference (RNAi) and insect pathogens. However, the biocontrol potential of defensins from the destructive rice pest Nilaparvata lugens (brown planthopper, BPH) remains largely unexplored. Here, we identified and functionally characterized a defensin-encoding gene NldefB in BPH. The open reading frame (ORF) of NldefB is 315 bp in length, encoding 104 amino acids with a conserved Knot1 domain. The qRT-PCR results showed that the transcription level of NldefB went upward with the increasing developmental stages, with the highest expressions in the female adults and their fat body. The expression of NldefB was continuously induced by bacterial pathogens but exhibited a pattern of initial increase followed by a decrease when challenged by a fungal pathogen Metarhizium anisopliae. RNAi-mediated silencing of NldefB significantly decreased the host survival rate, egg production and hatchability, as well as the capability to resist fungal infection. Additionally, NldefB suppression resulted in a significant increase in microbial loads. Our findings underscored that NldefB plays essential roles in regulating host development, pathogen defense, and microbial maintenance, providing a potential target for RNAi- and microbe-mediated BPH biocontrol.