A simple approach to fabricate chitosan-delivered avermectin controlled release microparticles for improved efficacy...

The presence of a synergistic effect between carrier and insecticide in controlled release formulations is highly desirable to improve efficacy to target pests and reduce insecticide use. Herein, controlled release microparticles of avermectin (AVM) were fabricated using natural chitosan (CTS) as a carrier by a pH adjustment method. The resulted AVM@CTS microparticles displayed high encapsulation efficiency (73.3 %), outstanding photostability, obvious pH/temperature sensitivity, and good deposition behavior on Chinese cabbage leaves. Instrument detections in combination with molecular dynamics simulations showed that AVM interacted with CTS mainly through physical adsorption, adhesion, and weak H-bonds. In vitro release data of the controlled release formulation obeyed the first-order kinetic equation. Toxicity tests exhibited a significantly synergistic effect between CTS and AVM, resulting in better quick-acting and long-term efficacy against Plutella xylostella larvae than that of the AVM acetone solution. The 72 h LC₅₀ of the formulation for a 21-day efficacy was 12.73 mg/L, much lower than the value (31.53 mg/L) of the AVM solution. Moreover, the AVM@CTS microparticles exhibited shorter half-life (19.6 days) than the unformulated AVM (23.0 days) under natural conditions in soil. This work contributes to the development of controlled release system with carrier-insecticide synergistic effect for sustainable pest control.