Is natural always safe? Effective botanical nano-aphicide can be harmful to pollinators

Abstract

Among the innovative and eco-friendly solutions to conventional pesticides, nano delivery systems (i.e., nanostructures and nano-emulsions) seem to be ideal candidates for botanical formulations to be used as insecticides. In this context, the proposed study aimed to formulate an Allium sativum EO-based nano-emulsion and to evaluate its toxicological activity against Aphis gossypii. Furthermore, the adverse effects of the nano-formulation on honeybees and plants were also investigated. The chemical composition of the garlic EO highlighted that the EO was composed only of sulfur compounds (95.35% of the total area). The nano-formulation (15% EO; 5% Tween® 80; 80% water w/w/v) was obtained using high-pressure microfluidization (HPM) techniques and physically characterized by dynamic light scattering (DLS). The results highlighted optimal physical properties with particle sizes ranging in the nanoscale (179 ± 1.4 nm), good polydispersity indices (PDIs), with values inferior to 0.25, and negative surface charge after 1 month of storage. The toxicological bioassays against the target pest showed high insecticidal activity with low estimated lethal doses in both residual contact toxicity (LD₃₀ of 0.810, LD₅₀ of 1.079, and LD₉₀ of 2.171% of EO) and topical application (LD₃₀ of 0.133, LD₅₀ of 0.212, and LD₉₀ of 0.667% of EO) after 72 h exposure. While negligible phytotoxic effects on sweet pepper plants were detected, the developed EO nano-emulsion revealed high toxicity towards honeybees through ingestion application. Overall, this study proved the high efficacy of the developed nano-biopesticide against the target pest; however, further studies are needed to fully understand the impact of these new nano-insecticides on non-target organisms in agroecosystems.