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

Among the innovative and eco-friendly solutions to conventional pesticides, nano delivery systems (i.e., nanostructures and nano-emulsions) seem to be the ideal candidates for botanical formulations to be used as insecticides. In this context, the proposed study firstly aimed to formulate an Allium sativum EO-based nano-emulsion and to evaluate its toxicological activity against Aphis gossypii. Furthermore, the adverse effects of nano-formulation on honeybees and plants were also investigated. The chemical composition of garlic EO highlighted that 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) and good polydispersity index (PDI), with values inferior to 0.25 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 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 the agroecosystems.