Lethal and sublethal effects of essential oil-loaded zein nanocapsules on a zoonotic disease vector mosquito, and their non-target impact

Recently the agrochemical industry is developing eco-friendly approaches based on the fabrication of biopesticides using substances, including biomass-borne products, with limited impact on human health and environment. One of these is the use of vegetable proteins, such as the corn-derived zein, as a safe nanocarrier loaded with bioactive compounds. Zein-based nanoparticles have been successfully applied to enhance the antimicrobial, antioxidant, repellent and insecticidal properties of hydrophobic substances such as essential oils (EOs). Herein, we developed two EO-loaded zein nanocapsules (NC) for mosquito larvicidal purposes. As active ingredients, we selected two Apiaceae essential oils (EO) with well documented insecticidal activities, i.e. Pimpinella anisum and Trachyspermum ammi, containing (E)-anethole and thymol as main constituents, respectively. The EO-based zein NC were prepared by self-assembly without using organic solvents, characterized for particle size by dynamic light scattering (DLS) and for stability over time and throughout stress conditions. EO-loaded zein NC showed high acute toxicity on Culex quinquefasciatus 3rd instar larvae. Sublethal toxicity following 1–5 h to the LC90 was noted in terms of larval and pupal mortality, emerged adult rate, and sex ratio. The NC ecotoxicological safety was demonstrated, showing limited non-target effects on aquatic (Daphnia magna) and terrestrial (Eisenia fetida) invertebrates, as also on vertebrate cells (human keratinocytes). Overall, the P. anisum and T. ammi EO-loaded zein NC may represent effective and eco-friendly formulations to be considered in mosquito control programs, pending field evaluation of their epidemiological impact.