Efficacy of garlic Essential oil-based nanoemulsion in controlling two crop key insect pests

The wide-scale use of synthetic chemicals is still the most influential pest management tool worldwide. Yet, insecticides have multiple undesired effects, e.g. production cost increase, side effects on non-target organisms and on the environment, pest resistance, human health risks. Thus, sustainable practices are strongly encouraged by public opinion and policy makers. Research efforts are oriented toward reducing the use of synthetic pesticides with natural molecules (biopesticides) with improved safety profiles. Encouraging results have been recently obtained testing botanicals, namely essential oils (EOs), against crop, stored product and medical/veterinary pests, and microbial pathogens. Laboratory trials were conducted to assess the insecticidal activity of garlic EO, formulated as nanoemulsion, against the cotton aphid, Aphis gossypii, and against eggs, larvae and adults of the South American tomato borer, Tuta absoluta. The potential toxic effects on tomato plants were also investigated. The tested EO was analysed by a gaschromatograph coupled with a triple quadrupole mass spectrometer (GC-MS-MS). Both the zeta potential (ζ) and particle size distribution of the formulation were assessed. More than 100 volatile compounds were identified and quantified. The EO was dominated by sulfurcontaining compounds, particularly allyl polysulfides. Indeed, diallylsulfide, –disulfide, -trisulfide and –tetrasulfide accounted for more than 80% of the total composition. The formulations developed had nanometric scale dimensions (180 nm) and good stability over time (ζ: -23.2mV). The nanoemulsion caused a higher contact toxicity at lower concentration for the tomato borer eggs compared with the cotton aphid, indeed the estimated LC90s were 4.41% and 16.14% for the two target pests, respectively. The bioactivity of garlic EO against T. absoluta was also confirmed at LC50 by causing 86.67±9.09% of larval mortality through ingestion and a significant oviposition deterrent effect in both choice and no-choice tests. Conversely, the nanoformulation did not cause any apparent phytotoxicity on tomato plants, thus suggesting a good potential for spray applications.