Physicochemical Characteristics of Four Limonene-Based Nanoemulsions and Their Larvicidal Properties against Two Mosquito Species, Aedes albopictus and Culex pipiens molestus

SIMPLE SUMMARY: The repeated use of synthetic insecticides against mosquitoes has posed negative impacts on the environment; hence, the utilization of more ecofriendly mosquito control products is deemed necessary. Nanoformulations of phytochemical substances with a safer profile for the environment have been considered potential larvicidal agents against mosquitoes. In this perspective, we formulated 4 (R)-(+)-limonene based oil-in-water nanoemulsions by low and high energy methods, and we studied their physicochemical characteristics (e.g., viscosity, stability, mean droplet diameter, polydispersity index). In addition, we evaluated their larvicidal properties against two mosquito species of great medical importance, Culex pipiens molestus and Aedes albopictus. Laboratory bioassays showed that limonene-based nanoemulsions either improved or did not affected limonene toxicity, depending on the delivery system and mosquito species. In conclusion, all tested limonene-based nanoemulsions provided sufficient toxic effects against mosquito larvae, serving as potential formulations for mosquito control applications. ABSTRACT: Negative impacts on the environment from the continuous use of synthetic insecticides against mosquitoes has driven research towards more ecofriendly products. Phytochemicals, classified as low-risk substances, have been recognized as potential larvicides of mosquitoes; however, problems related to water solubility and stability are limiting factors for their use in mosquito control programs in the field. In this context, many researchers have focused on formulating essential oils in nanoemulsions, exploiting innovative nanotechnology. In the current study, we prepared 4 (R)-(+)-limonene oil-in-water nanoemulsions using low and high energy methods, and we evaluated their physicochemical characteristics (e.g., viscosity, stability, mean droplet diameter, polydispersity index) and their bioactivity against larvae of two mosquito species of great medical importance, namely, Cx. pipiens molestus and Ae. albopictus. According to the dose–response bioassays with the limonene-based nanoemulsions and pure limonene (dissolved in organic solvent), the tested nanoformulations improved the activity of limonene against Ae. albopictus larvae, while the performance of limonene was either the same or better than limonene against Cx. pipiens molestus, depending on the applied system. Overall, we achieved the production of limonene-based delivery nanosystems, with sufficient lethal properties against mosquito larvae to consider them promising larvicidal formulations applicable to mosquito breeding sites.