Effects of essential oil-based formulation on biopesticide activity

Essential oils (EOs) represent a promising source of biopesticides, given their compositional complexity which bestows them high insect specificity and low risk of inducing resistance. However, their use in agriculture remains limited by their rapid degradation, limited duration of effect and non-target toxicity. These issues largely result from the under-optimized methods currently used to formulate EOs, in which their volatile organic compounds (VOCs) are poorly protected. In this study we compared pure Artemisia and Rosemary EOs to EOs formulated in three, low-cost, relatively simple, and easily applicable manners: as nanoemulsions, atomized powders, and Natural Deep Eutectic Solvents (NaDES). 24 hours after formulation, the entomotoxicity and phytotoxicity of the EOs were tested on Bemisia tabaci infested tomato plants. The identity and relative abundance of VOCs present in all formulations were also assessed 24 hours post-preparation using GC-MS and GC-FID. Nanoemulsions proved the most entomotoxic of formulations, followed by NaDES and pure EOs, while atomized powders were not significantly more entomotoxic than the control. Entomotoxicity was coupled with phytotoxicity for all formulations, except NaDES which induced particularly high rates of B. tabaci mortality when prepared with Rosemary EO, in addition to reducing damages on treated plants. Total VOC abundance depended on VOC release kinetics, determined by formulation, which although higher for pure EOs, was more gradual for NaDES. These results show the importance of EO formulation and the potential for NaDES to provide effective, sustained pest control.