Exploring garlic nano-emulsions for Tuta absoluta control, their impact on the intestinal microbiome and their side effects on Nesidiocoris tenuis

The South American tomato pinworm, Tuta absoluta Meyrick, is a major destructive pest on tomato crops. Currently, the management of this pest in both field and greenhouse settings relies mainly on synthetic insecticides. However, concerns regarding the indiscriminate use of these insecticides, coupled with the growing demand for safer and more environmentally friendly solutions, have driven researchers to explore alternative pest control strategies. Among the potential options, essential oils (EO) have shown significant promise, with nanoemulsions (NE) further enhancing their stability and effectiveness. The main goal of this study was to develop garlic nano-emulsions with a high active ingredient concentration and a low surfactant percentage, ensuring long-term stability and small particle size. This was accomplished using both low (LP)- and high (HP)-pressure microfluidization techniques. The LP nano-emulsion was produced at 2,000 psi, while the HP nano-emulsion was achieved at 20,000 psi. The synthesized nanoemulsions were tested in laboratory conditions to evaluate their toxic effects on T. absoluta larvae, their impact on the predator Nesidiocoris tenuis, and their potential phytotoxicity on tomato plants. Both nanoemulsions exhibited a low polydispersity index (PDI) with high stability over time. The two nanoformulations demonstrated significant toxicity against second-instar larvae of T. absoluta 72 hours after treatment, with an LD90 of 0.886 g/L for the LP nanoformulation and 1.062 g/L for the HP nanoformulation. In addition, 100% mortality was observed in larvae exposed to the highest concentration of treatments. In bioassays on N. tenuis, adult mortality at 72 hours was low, less than 20% for both nanoemulsions. In phytotoxicity tests, the HP nanoemulsion exhibited low levels of phytotoxicity, while the LP nanoemulsion caused 33% damage to tomato plants at the LD90 concentration. Additionally, this study explored for the first time the intestinal microbiome of T. absoluta larvae exposed to garlic nanoemulsions, revealing significant differences between treated and untreated samples, suggesting a direct effect of the EO treatments on the bacterial communities. The results of this study indicate that garlic nanoemulsions could be an effective option for managing T. absoluta populations in the field. However, further research is needed to develop and test formulations that ensure minimal phytotoxicity.