Eugenol and Pulegone as potential biorational alternatives for Trioza erytreae (Hemiptera: Triozidae) control: Preliminary results on nymphal toxicity and applicability on Citrus limon

Agricultural activity relays deeply on the usage of synthetic insecticides for pest control, however, the extensive use or misuse of these substances can have negative impacts on the environment, human health and even on agricultural ecological subsystems. Essential oils (EOs) are secondary metabolites synthesized in plant secretory structures that are less hazardous to the environment and safer to handle, with known effectivity against arthropods, thus presenting a viable eco-friendly alternative for typical synthetic insecticides. Trioza erytreae (Del Guercio) (Hemiptera: Triozidae) is a major threat for citrus production, expanding rapidly throughout the Iberian Peninsula. To this day, no effective control method to sustainably control T. erytreae populations has thus far been obtained and the effects of EOs on this pest have not yet been documented. In this study, the insecticidal potential of EOs active compounds Eugenol (99 %), Pulegone (85 %) and their combination was assessed by determining their toxicity through topical application on T. erytreae nymphs and their phytotoxicity on Citrus limon ((L.) Burm.), T. erytreae preferred host, in laboratory conditions. Pulegone was more toxic to T. erytreae nymphs than Eugenol, showing the lowest LD₅₀ values both after 24 h (0.005 µL nymph⁻¹) and 48 h (0.003 µL nymph⁻¹) whereas for the LD₉₀, the combination of both oils was the most toxic both after 24 h (0.020 µL nymph⁻¹) and 48 h (0.012 µL nymph⁻¹). On concentrations equal or lower than 3.60 %, Eugenol presented the highest phytotoxic effect. In concentrations that did not pose a significant phytotoxic effect on C. limon, the combination of both active compounds exhibited the highest nymphal mortality. The beneficial integration of both Eugenol and Pulegone in a mixture was shown to be the best approach for utilizing these compounds, but care in their concentrations must be taken, given the possible effects on phytotoxicity. This preliminary study presents new insights on the potential effects of EOs on T. erytreae and their applicability in citrus crops, thus making an entry way for the development of more sustainable control strategies for this pest control.