Preparation and Characterization of Efficient and Safe Rotenone Solid Nanodispersion by Self-Emulsifying Technique

Self-emulsifying solid nanodispersion technology is emerging as an attractive strategy to prepare new eco-friendly and efficient nano-formulations due to its simple, energy efficient and easy scale-up process. However, it is still unknown whether this technology can be employed to cope with the drawbacks of botanical insecticides including poor water solubility, rapid photodegradation and limited targeting efficiency. In this study, rotenone (Rot) was selected as a model of botanical insecticides and its solid nanodispersion (Rot–SND) was prepared by a self-emulsifying method combined with parameter optimization. Our target nano-formulation, consisting of 5% Rot, 20% complex surfactants of 8% Ethylan 992 and 12% EL–80, and 75% lactose, exhibited excellent storage stability and significantly improved the pseudo-solubility of Rot by at least 250 times. The average particle size and polydispersity index (PDI) of Rot–SND were 101.19 nm and 0.21, respectively. Rot–SND displayed smaller contact angles and greater retention on both cucumber and cabbage leaves than those of the commercial emulsifiable concentrates (EC). Rot–SND was also more resistant to photodegradation with a degradation rate reduced by 27.01% as compared with the EC. In addition, the toxicity of Rot–SND towards Aphis gossypii was 3.25 times that of the EC, with a median lethal concentration (LC50) of 1.26 µg a.i./mL. Under the field conditions, Rot–SND showed a prolonged duration for A. gossypii control, with a significantly higher control efficacy (88.10%) on the 10th day than that of the EC (77.02%). Moreover, a 2.88-fold decline in the toxicity towards nontarget mosquito larvae was observed for Rot–SND as compared with the EC. Overall, for the first time, our results indicated the role of Rot–SND as an eco-friendly and efficient way to improve the solubility, foliar affinity, photostability, bioactivity and eco-safety of Rot. This research provides a feasible strategy to prepare more eco-friendly botanical pesticide formulations of high efficiency.