Evaluation of the Stability of a 1,8-Cineole Nanoemulsion and Its Fumigant Toxicity Effect against the Pests Tetranychus urticae, Rhopalosiphum maidis and Bemisia tabaci

SIMPLE SUMMARY: Pests are largely responsible for the loss of agricultural crops, so the search for new pesticides for their control is indispensable. The irrational use of synthetic products has affected human health and the environment, and has generated resistance, which is why the use of natural products could be a safer alternative. In this study, the formulation of a nanoemulsion was carried out to provide greater stability to the botanical compound 1,8-cineole, whose pesticidal effect is documented; however, it is not used due to its high volatility. The pesticidal effect of this nanoemulsion was also evaluated against the pests known as two-spotted spider mite, corn aphid and silverleaf whitefly. Nanotransport systems such as nanoemulsions allows for the field application of molecules that are chemically unstable on their own, such as monoterpenoids. With this study it was possible to determine that these nanoemulsion systems favor the release of the active compound in laboratory tests, increasing the mortality rate of the three pests. This allows for proposing this nanoemulsion as a potential botanical pesticide product against agricultural arthropod pests. ABSTRACT: Pest control is a main concern in agriculture. Indiscriminate application of synthetic pesticides has caused negative impacts leading to the rapid development of resistance in arthropod pests. Plant secondary metabolites have been proposed as a safer alternative to conventional pesticides. Monoterpenoids have reported bioactivities against important pests; however, due to their high volatility, low water solubility and chemical instability, the application of these compounds has been limited. Nanosystems represent a potential vehicle for the broad application of monoterpenoids. In this study, an 1,8-cineole nanoemulsion was prepared by the low energy method of phase inversion, characterization of droplet size distribution and polydispersity index (PDI) was carried out by dynamic light scattering and stability was evaluated by centrifugation and Turbiscan analysis. Fumigant bioactivity was evaluated against Tetranychus urticae, Rhopalosiphum maidis and Bemisia tabaci. A nanoemulsion with oil:surfactant:water ratio of 0.5:1:8.5 had a droplet size of 14.7 nm and PDI of 0.178. Formulation was stable after centrifugation and the Turbiscan analysis showed no particle migration and a delta backscattering of ±1%. Nanoemulsion exhibited around 50% more bioactivity as a fumigant on arthropods when compared to free monoterpenoid. These results suggest that nanoformulations can provide volatile compounds of protection against volatilization, improving their bioactivity.