Size-dependent Effect on Foliar Utilization and Biocontrol Efficacy of Emamectin Benzoate Delivery Systems

The development of nanopesticides provides new avenues for pesticide reduction and efficiency improvement. However, the size effect of nanopesticides remains unclear, and its underlying mechanisms of influence have become a major obstacle in the design and application of pesticide nanoformulations. In this research, the noncarrier-coated emamectin benzoate (EB) solid dispersions (Micro-EB and Nano-EB) were produced under a constant surfactant-to-active ingredient ratio by a self-emulsifying-carrier solidification technique. The particle size of Micro-EB was 162 times that of spherical Nano-EB. The small size and large specific surface area of Nano-EB facilitated the adsorption of surfactants on the surface of the particles, thereby improving its dispersibility, suspensibility, and stability. The pinning effect of nanoparticles significantly suppressed droplet retraction and rebounding. Moreover, Nano-EB exhibited a 25% higher retention of the active ingredient on cabbage leaves and a 70% higher washing resistance than Micro-EB, and both were significantly different. The improvement of abilities in wetting, spreading, and retention of Nano-EB on crop leaves contributed to the increase in foliar utilization, which further resulted in a 1.6-fold enhancement of bioactivity against target Spodoptera exigua compared to Micro-EB. Especially, Nano-EB did not exacerbate the safety risk to the nontarget organism zebrafish with no significant difference. This study elaborates the size effect on the effectiveness and safety of pesticide formulations and lays a theoretical foundation for the development and rational utilization of efficient and environmentally friendly nanopesticides.