Formulation of Ethyl Cellulose Nanoparticles Encapsulated with Osthole Provides Long-Lasting Plant Protection against a Major Pest Mite

The broader use of botanical pesticides has been limited by shorter residual activity on plants, slower onset of action, and higher costs compared with conventional pesticides. These challenges could be overcome by the development of simple, cost-effective, and long-lasting preventive nanocomposites for botanical pesticides. In this study, we successfully developed a low-cost ethyl cellulose (EC)-based delivery system for the botanical pesticide osthole (OST), designed to provide extended preventive protection against Tetranychus urticae infestations. A comparative analysis of the three nanocomposites (graphene oxide (GO)-OST, EC-OST, and chitosan (CS)-OST) revealed that EC-OST exhibited superior thermal stability, UV resistance, controlled release of the OST payload, and strong acaricidal activity. The degradation of OST on leaf surfaces was reduced by encapsulation in EC, while its penetration into plant tissues was improved. When EC-OST was applied to leaves, an increase in T. urticae mortality, a reduction in reproduction and egg adhesion, and impairment of feeding behavior through extended searching and feeding times were observed. The peak occurrence of T. urticae infestation was delayed by 10 days following the preventive application of EC-OST, reducing plant damage and protecting the plants for more than 20 days. This nanoinsecticide allows for low-frequency OST application, reducing farmers’ production costs, and increasing profitability, thereby offering great potential for promoting the use of botanical pesticides in plant protection.