Nanoformulation enhances emamectin action in study

Researchers have developed a disaggregation strategy to produce a nanopesticide from emamectin benzoate without nanocarriers and without surfactants. The method uses acetic acid in aqueous suspension and generated particles with an average diameter of 7 nanometers. The study reports increased bioactivity against Megalurothrips usitatus and Meloidogyne enterolobii, in addition to greater penetration into cowpea leaves and bell pepper roots.

The study evaluated the direct effect of size reduction on pesticide biointeractions. According to the researchers, most nanopesticides involve nanocarriers or surfactants. These components can alter the interaction with organisms and make it difficult to distinguish between the effect of size and the effect of formulation.

Acetic Acid

In the tested strategy, acetic acid broke hydrogen bonds present in emamectin benzoate aggregates. Analysis indicated the absence of a chemical reaction and the absence of a stable complex between acetic acid and the active molecule. The process generated a stable colloidal dispersion called HOAc-EB.

The formulation showed stability after 14 days at 0 degrees Celsius, 25 degrees Celsius, and 55 degrees Celsius. It also maintained particle size after three freeze-thaw cycles. The active ingredient content did not differ from conventional emamectin benzoate under the evaluated conditions.

In bioassays, HOAc-EB reduced the median lethal concentration by 91 percent compared to Megalurothrips usitatus. The value dropped from 3,02 milligrams per liter to 0,280 milligrams per liter. Against Meloidogyne enterolobii, the median lethal concentration fell 56 percent, from 18,5 milligrams per liter to 8,1 milligrams per liter.

Use by the plant

The researchers also evaluated the plant's use. On cowpea leaves, the contact angle of the HOAc-EB droplet reached 66,3 degrees, compared to 87,8 degrees for conventional emamectin benzoate. The surface tension dropped from 64,1 millinewtons per meter to 53,1 millinewtons per meter. The result indicates better spreading of the spray solution on the leaf surface.

In soil, HOAc-EB showed lower adsorption. Conventional emamectin benzoate showed complete adsorption within 24 hours at concentrations below 250 milligrams per liter of active ingredient. HOAc-EB showed complete adsorption only at 62,5 milligrams per liter. At 250 milligrams per liter, adsorption was below 10 percent.

Translaminar penetration

Translaminar penetration also increased. In cowpea leaves, the peak of active ingredient accumulated with HOAc-EB reached 1,29 milligrams per gram at 25 minutes. This value exceeded the result of conventional emamectin benzoate by 5,1 times, which was 0,21 milligrams per gram at 30 minutes.

In bell pepper roots, the peak accumulated active ingredient reached 1,09 milligrams per gram at 25 minutes with HOAc-EB. This result exceeded the value observed with the conventional formulation by 4,4 times, which was 0,20 milligrams per gram. Despite this improvement, the compound did not exhibit systemic behavior. The active ingredient remained at the application site on leaves and roots.

Field trials showed differences depending on the target. In the control of Megalurothrips usitatus in cowpea, the number of thrips per flower dropped to 5,5 after 48 hours with HOAc-EB. The conventional treatment recorded 7,1 individuals per flower. Statistical analysis did not indicate a significant difference between the two treatments.

Nematode control

In control of Meloidogyne enterolobii in bell peppers, the difference was most noticeable. The conventional treatment recorded 80,7 galls per gram of root, a value with no statistically significant difference compared to the control, which had 72,0 galls per gram of root. The HOAc-EB treatment reduced the number to 37,6 galls per gram of root.

Safety assessments did not indicate increased toxicity in non-target organisms. In cowpea, repeated spraying with 1000 milligrams per liter for 14 days did not cause visible symptoms of phytotoxicity. In bell pepper, a single root drench application at the same concentration also did not cause visual growth inhibition during the observed period.

Tests with zebrafish, earthworms, and mice indicated similar toxicity between HOAc-EB and conventional emamectin benzoate. The researchers report no increase in toxicity after size reduction.

The study also points to operational feasibility. The formulation with up to 30 percent active ingredient was obtained by simply mixing emamectin benzoate, acetic acid, and water. The process eliminates the need for high-energy milling, organic solvents, and external surfactants.

Further information can be found at doi.org/10.1002/advs.75914