Nanotechnology applied to development of synthetic acaricides associated with plants compounds for the Rhipicephalus (Boophilus) microplus control

Rhipicephalus microplus causes declines in cattle production and consequent damage to livestock. The resistance of ticks and the risk of the presence of residues in food of animal origin have driven the search for new control alternatives. Several plant compounds have an acaricidal/repellent potential, however, they have limitations in their application. Nanocarriers can protect these compounds, increase their aqueous solubility and bioavailability, and reduce possible toxic effects. Thus, the objective of this study was to develop acaricide formulations from Solid Lipid Nanoparticles (NLS), Nanostructured Lipid Carriers (CLN) and Zein Nanoparticles (NZ), associated with cypermethrin (cip), chlorpyrifos (clo) and a plant compound (citral, menthol or limonene), characterize these nanocarrier systems and verify their performance against larvae and engorged females of R. microplus. Nine formulations were developed and characterized by Dynamic Light Scattering (DLS) and Nanoparticle Tracking Analysis (NTA). The formulations 1 (NLS+cip+clo+citral), 2 (NLS+cip+clo+menthol), 3 (NLS+cip+clo+limonene), 4 (CLN+cip+clo+citral), 5 (CLN+cip+clo+menthol) and 6 (CLN+cip+clo+limonene) obtained mean diameters from 286 to 304 nm; polydispersion from 0.16 to 0.18; zeta potential from -15.8 to -20 mV, concentration from 3.37 ± 0.24 x 1013 to 5.44 ± 0.18 x 1013 particles/mL; and Encapsulation Efficiency (EE) > 98.01% for all active ingredients, while, for the same parameters, zein formulations NZ-1 (NZ+cip+clo+citral), NZ-2 (NZ+cip+clo+menthol) and NZ-3 (NZ+cip+clo+limonene) obtained, respectively, mean values of: 282.18 to 290.64 nm; 0.24 to 0.25; -3.35 to -6.10 mV; concentration of 2.73 ± 2.67 x 1013 to 3.20 ± 3.03 x 1013 particles/mL and EE> 96%. All formulations were evaluated for their acaricidal potential and compared with positive (Colosso®) and negative (distilled water; and nanoparticles without active ingredient) controls. In the evaluation of lipid nanocarrier formulations, by the Larval Pack Test (TPL), the negative controls did not cause mortality of the larvae, while the positive control, evaluated at the concentration of 0.512 mg.mL-1 , caused 100% mortality. The formulations of NLS 1, 2, 3 and CLN 4, 5 and 6 were evaluated from 0.004 to 0.466 mg.mL-1 . At the concentration of 0.007 mg.mL-1 they reached 90.4, 75.9, 93.8, 100, 95.1, 72.7% of mortality. With the exception of 4, for which it was not possible to determine lethal concentrations (CL), formulations 1, 2, 3, 5 and 6 resulted in CL50 and CL90 of: 0.0033 and 0.0072; 0.0054 and 0.0092; 0.0040 and 0.0081; 0.0023 and 0.0054; 0.0055 and 0.0094 mg.mL -1 , respectively. Regarding the zein nanoformulations evaluated by the TPL, the negative controls also did not cause mortality of the larvae, however, the positive control (evaluated from 0.004 to 0.512 mg.mL-1 ), resulted in larval mortality > 71.9% in the concentration 0.064 mg.mL-1 , while zein formulations (evaluated from 0.004 to 0.466 mg.mL-1) caused mortality> 80% in the concentration of 0.029 mg.mL-1 . These formulations NZ-1 (NZ + cip + clo + citral), NZ-2 (NZ + cip + clo + menthol) and NZ-3 (NZ + cip + clo + limonene) still resulted in high larval mortality rates in lower concentrations, with LC50 and LC90 of: 0.0136 and 0.0352; 0.0115 and 0.0386; 0.0117 and 0.0301 mg.mL-1 , respectively, and 0.0319 and 0.1028 mg.mL-1 , respectively, for the positive control). The zein formulations were also evaluated by the Adult Immersion Test (TIA) and the formulations NZ-1, NZ-2 and NZ-3 obtained, respectively: 50.2, 40.5 and 60.1% efficacy on engorged females at a concentration of 0.466 mg.mL-1 , while the positive control resulted in 39.4% efficacy at 0.512 mg. mL-1 . The zein formulations still showed a high residual activity, although less than that of the positive control. This study demonstrated that it was possible to encapsulate the prioritized active ingredients and characterize the carrier systems. All nanoformulations were able to protect the active ingredients against degradation in solution, which is a characteristic of stability aimed at commercial tick products. Thus, nanoformulations can be an alternative for the development of new biocarpathicides with less active ingredients, aiming to promote safer parasitic control, with less risk of the presence of residues in food of animal origin and in the environment. (AU)