Bioactivity of Allium sativum essential oil-based nano-emulsion against Planococcus citri and its predator Cryptolaemus montrouzieri

Botanical extracts, in particular essential oils (EOs), could be the ideal candidates for the development of biopesticides as an alternative to synthetic pesticides. However, some limitations of EOs (high flammability, volatility, degradability, poor solubility in water) prevent their use under real operational conditions. Nanotechnologies are useful tools to overcome the above-mentioned limitations of these natural substances. Furthermore, encapsulation in nano-delivery systems (nanoparticles and nano-emulsions) can improve the functional properties of EOs. In this context, this study aimed to develop a highly stable, concentrated garlic nano-emulsion (15%) and to evaluate the acute toxicity with different exposure routes towards Planococcus citri and its predator Cryptolaemus montrouzieri. First, garlic EO was used to develop a nano-emulsion (15% EO; 5% Tween 80; 80% water) using a high-pressure microfluidizer; then both the crude EO and EO in nano-emulsion were chemically investigated by Solid Phase Microextraction-Gas Chromatography-Mass Spectrometry (SPME-GC-MS) technique. The nano-emulsion was physically characterized by dynamic light scattering analysis over time (24 h, 3 months and 1 year after preparation) and used in bioassays involving both the target and non-target organisms. Results showed that the garlic EO consisted of over 95% sulphur compounds with diallyl disulphide as the most abundant component, and the developed nano-emulsion remained stable even after 1 year, with droplets’ dimension within the nanometric range (221.4 nm). The nano-formulation was effective against the target pest after 48 h from the treatment (Direct: LC90 = 0.967%; Indirect: LC90 = 1.088%), while it had no effect on C. montrouzieri. These promising results highlight the potential of garlic-based nano-emulsion as effective and environmentally friendly insecticide for pest control.