Garlic EO-based nano-emulsion in pest management: formulation and biological activity on target and non-target organisms

Among botanicals used as insecticides, essential oils (EOs) attract the interest of different stakeholders despite some of their intrinsic properties limiting their use in real field conditions. In this scenario, the use of nanotechnologies seems a promising tool to overcome these drawbacks.

Our research aimed to develop garlic EO-based nano-emulsion with a high EO–surfactant ratio (3: 1) and conduct an insecticidal evaluation against different citrus pests. The biological effects on different non-target organisms (pollinators and predators) were also investigated.

Garlic EO was chemically analysed (GC-MS) and formulated as a nano-emulsion through the use of a high-pressure microfluidizer apparatus (HPM). The resulting formulation (15% EO; 5% Tween® 80; 80% water) was physically characterized (i.e. size, PDI and surface charge) using dynamic light scattering (DLS) analysis. Garlic EO was composed of sulphur compounds (96.3%), and diallyl disulphide was the most abundant one (37.26%). The optimal physical properties of the developed formulation (size < 250nm; PDI < 0.2, and negative surface charge) were maintained for up to 1 year.

The efficacy against target pests showed high insecticidal activity, with an estimated LD₉₀ always less than 2.5 % of EO against all the tested insects. On the other hand, the garlic nano-emulsion was completely safe against non-target insects and showed no phytotoxic effects on citrus plants. Plants treated with the formulated nano-emulsion overexpressed different genes involved in plant defence, suggesting a dual benefit effect (insecticidal activity and enhancement of plant defence) of this formulation.

Overall, the high insecticidal activity, the absence of adverse effects on non-target organisms, and the beneficial effects on plants suggest the potential use of this formulation in organic and/or integrated pest management programmes.