A floral resource enhances parasitoid-mediated pest control and increases rice yields

Global rice production that exceeds 500 million tonnes annually currently provides a staple food for over 3 billion people. Its production has a high dependency on insecticides leading to diffuse pollution, impacts on biodiversity and reductions in critical ecosystem services. Through a four-year field experiment, we demonstrated that planting the annual flower Zinnia elegans along paddy field ridges significantly strengthens biological control provided by a hymenopteran egg parasitoid (Trichogramma japonicum). This is a key natural enemy of the striped stem borer (Chilo suppressalis) and rice leaf folder (Cnaphalocrocis medinalis), both major lepidopteran rice pests. Field trials showed that the combination of this flower with active releases of the parasitoid achieved pest suppression rates exceeding 81%, outperforming other tested interventions. Complementary laboratory experiments suggest that this may be mechanistically underpinned by nectar resources increasing adult parasitoid longevity (by 47.1–55.8%) and parasitic capacity (by 37.2–41.7%). Spatial layout field experiments also identified that the width of both flower strips and the rice paddy plots influenced the magnitude of pest control. Finally, we used a two-year demonstration study to show that flower strip establishment combined with parasitoid release led to a 60% reduction in conventional number of insecticide applications as well as average control efficacies of 92.4% for stem borer and 93.1% for leaf folder, respectively. This integrated pest management strategy surpassed the performance of the full dose insecticide regime, while also increasing spider density by 56.7%, reducing pest rice planthopper density by 19.7%, and raising rice yields by 6.9% (to 7077.5 kg ha−1). This increased the net economic benefit by 10.1% (to 45,096.1 Chinese Yuan (CNY) ha−1). Our findings reveal a practical, scalable approach that harnesses floral-resource provisioning that promotes biocontrol, curbs pesticide inputs, and delivers robust agronomic and ecological gains.