Preparation, characterisation, and controlled release of sex pheromone-loaded MPEG-PCL diblock copolymer micelles for Spodoptera litura (Lepidoptera: Noctuidae)

Sex pheromones are important for agricultural pest control. The main sex pheromone components of Spodoptera litura are (Z,E)-9,11- and (Z,E)-9,12-tetradecadienyl acetate (Z9,E11-14:Ac; Z9,E12-14:Ac). In this study, we investigated the optimal conditions for encapsulation of S. litura sex pheromonesin micelles via the self-assembly method using monomethoxy poly (ethylene glycol)-poly (ε-caprolactone) (MPEG-PCL) as a biodegradable wall-forming material with low toxicity. In the L(9)(3(4)) orthogonal experiment, 3 amphiphilic block copolymers, with different hydrophilicity to hydrophobicity ratios, were examined. Optimal encapsulation conditions included stirring of MPEG(5000)-PCL(2000) at 1000 rpm at 30°C with 2.5:1 wall-forming: core material mass ratio. S. litura sex pheromone-loaded MPEG(5000)-PCL(2000) micelles presented a homogeneous spherical morphology with apparent core-shell structure. The release kinetics of optimized MPEG(5000)-PCL(2000) micelles was best explained by a first-order model. Encapsulated Z9,E11-14:Ac and Z9,E12-14:Ac were released slowly, not suddenly. Methyl oleate (MO) was used as an agent to control micellar release performance. When MO content equalled block content, micelle half-life could be prolonged, thereby controlling the release speed. Overall, our results showed MPEG-PCL as a promising controlled-release substrate for sex pheromones.