A multi-bioactive pesticide delivery nanosystem for precise and efficient management of pest stresses in rice

Rice production is increasingly threatened by simultaneous insect and fungal stresses, yet conventional pesticide applications suffer from low utilization, poor systemic mobility, and limited ability to manage multiple biotic pressures. Nanodelivery systems offer potential improvements but often face limitations such as low loading, single functionality, or dependence on synthetic adjuvants.

This study aimed to develop a multifunctional, carrier-free nanopesticide capable of efficient delivery, systemic transport, and immune activation, and to evaluate its ability to control insect-pathogen co-stress in rice.

An amphiphilic conjugate, chitosan oligosaccharide-4-fluorophenoxyacetic acid (COS-4-FPA), was synthesized and used to self-assemble with emamectin benzoate (EB) in water to form EB@COS-4-FPA nanoparticles. Physicochemical characterization, photostability, foliar adhesion, and bidirectional transport were evaluated using DLS, TEM, HPLC, and CLSM. Bioassays evaluated insecticidal activity against Chilo suppressalis and Cnaphalocrocis medinalis, while plant-mediated resistance to Nilaparvata lugens and Magnaporthe oryzae was assessed through induced-defense assays. Transcriptome profiling and qPCR elucidated molecular mechanisms, and biosafety was examined in rice seedlings and zebrafish.

EB@COS-4-FPA integrates efficient delivery (strong leaf adhesion, UV stability, and systemic translocation), enhanced insecticidal activity against concealed pests (Chilo suppressalis and Cnaphalocrocis medinalis) in laboratory and field trials, and host-defense activation that confers additional resistance against Nilaparvata lugens and Magnaporthe oryzae. Importantly, the formulation step proceeds in water without extra organic solvents or surfactants, and reduced acute toxicity in zebrafish highlights its environmental compatibility.

EB@COS-4-FPA integrates high-efficiency delivery with endogenous immune activation, enabling durable and systemic protection against diverse biotic stresses. This work establishes a green, multifunctional nanoplatform for sustainable pest and disease management in rice.