The indiscriminate use of synthetic insecticides has led to contamination of the environment, resurgence of pests, and the development of resistance in key agricultural pests. Aphis gossypii, or the cotton aphid, is a highly damaging sap-sucking insect pest of cotton and several horticultural crops. Botanical insecticides such as neem oil provide eco-friendly alternatives; however, their stability and bioavailability in conventional formulations are a concern. The aim of the present study was to formulate a stable neem oil nanoemulsion and assess its insecticidal efficacy against A. gossypii under laboratory and semi-field conditions.

Neem oil nanoemulsion was prepared by high-speed homogenization with Tween 80 as the surfactant. The formulation was characterized for droplet size, polydispersity index (PDI), zeta potential, and storage stability. Laboratory bioassays were performed by the leaf dip method at four concentrations (0.5-2%). Mortality was recorded at 24, 48, and 72 h. LC₅₀ values were calculated by probit analysis. Semi-field trials were conducted on potted cotton plants.