A carrier-free nanopesticide shows when smaller pesticide particles improve pest control and when additives, not size, may explain the gains.
(Nanowerk Spotlight) Nanopesticides have promised better pest control, but many studies cannot prove whether the benefit comes from being nanoscale or from the chemical scaffolding used to make them nanoscale. Carriers, surfactants, polymer shells, and other formulation aids can change how a pesticide spreads, dissolves, penetrates plant tissue, and interacts with organisms. Those additives may improve performance, but they also make it harder to tell whether nanoscale size was the reason.
That cause-and-effect problem sits behind many claims for agricultural nanotechnology, including recent work on nanoscale pesticide delivery systems that aims to place crop-protection chemicals more precisely. If a carrier helps the active ingredient stick to a leaf, or a surfactant helps it cross a biological barrier, better pest control cannot prove that size itself did the work.
Instead of building a delivery vehicle around emamectin benzoate, the researchers used acetic acid to pull apart the pesticide’s own aggregates in water. The process produced stable, carrier-free particles about 7 nm across without forming a lasting complex between the acid and the pesticide.
The interpretation depends on whether acetic acid merely disperses the pesticide or becomes part of a new delivery structure. Spectroscopic data showed no major chemical change in emamectin benzoate after treatment. Simulations traced the breakup to disrupted hydrogen bonding among the pesticide’s molecular components. Acetic acid weakened the interactions that hold the clusters together, allowing the active ingredient to persist as nanoscale colloidal particles without becoming a persistent carrier around it.
Compared with untreated emamectin benzoate, the nanosized formulation became more active against both target organisms tested. It lowered the 24 h LC₅₀ by 91 % against Megalurothrips usitatus, a thrips pest of cowpea, and by 56 % against Meloidogyne enterolobii, a root-knot nematode that damages chili pepper roots. In both cases, less active ingredient produced the same lethal effect in laboratory tests.
The improved activity matched changes in how the pesticide met plant and soil barriers. HOAc-EB spread more readily on cowpea leaves, giving droplets better contact with the waxy surface. It also entered cowpea leaves 5.1-fold more effectively and chili pepper roots 4.4-fold more effectively at peak uptake. Reduced aggregation and stronger local penetration increased the amount of active ingredient available near likely feeding sites.
Field tests show where nanosizing helped and where it did not. HOAc-EB, the carrier-free nanopesticide, significantly reduced root galling caused by the root-knot nematode Meloidogyne enterolobii in chili pepper. In cowpea, it reduced thrips numbers compared with the untreated control, but did not significantly outperform conventional emamectin benzoate. The result shows that smaller pesticide particles can improve control when they overcome a specific delivery barrier, such as soil binding, but they do not automatically improve every field outcome. (Image: Reproduced from DOI:10.1002/advs.75914, CC BY) (click on image to enlarge)
Conventional emamectin benzoate binds strongly to soil, which can trap the active ingredient before it reaches roots or soil-dwelling pests. HOAc-EB showed lower adsorption and greater desorption. The nanoscale form did not become freely mobile under all soil conditions, but it reduced an important loss pathway for nematode control.
Nanosizing did not rewrite the pesticide’s transport behavior inside plants. Emamectin benzoate has translaminar activity, meaning it can move into nearby plant tissue after application, but it does not travel systemically throughout the plant. HOAc-EB increased local penetration into treated tissues, yet it did not create long-distance transport from leaves to roots or from roots to leaves.
Field trials exposed the difference between solving a delivery bottleneck and improving every use case. In chili pepper, HOAc-EB significantly reduced root galling caused by Meloidogyne enterolobii, while conventional emamectin benzoate performed no better than the untreated control. Reduced soil binding helped more active ingredient reach the nematode, matching the soil and root-penetration results.
The cowpea trial gave a narrower outcome. HOAc-EB reduced thrips numbers compared with the untreated control, but it did not significantly outperform conventional emamectin benzoate. Laboratory bioactivity remained real, but field efficacy depended on exposure, application coverage, pest behavior, crop structure, weather, and timing, not only on particle size.
Nanosizing helped when the performance problem came from barriers that smaller particles could change, such as aggregation, surface contact, soil binding, or local tissue entry. It did not act as a general upgrade that automatically improved every field outcome. This restraint matters because environmental questions around nanopesticides remain tied to dose, exposure route, soil behavior, and organism-specific effects.
HOAc-EB caused no visible crop injury at 1000 mg⋅L⁻¹ in the reported cowpea and chili pepper assays. Tests with zebrafish, earthworms, and mice did not show greater toxicity in the nontarget species tested. These assays do not replace a full environmental risk assessment, especially for repeated agricultural use across different soils and ecosystems. They show that higher target activity did not come with broader increases in measured nontarget toxicity in this test set.
Many nanopesticide designs look promising in controlled tests but carry manufacturing burdens. HOAc-EB avoided several of them. It remained stable under different storage temperatures and freeze-thaw cycling, mixed compatibly with several commercial pesticide formulations, and reached active ingredient loading as high as 30 %. Higher loading could reduce water volume, packaging, storage, and transport demands compared with more dilute water-based products.
The preparation method relies on simple mixing in water, without high-energy grinding, organic solvents, surfactants, or engineered carriers. The paper estimates that acetic acid would add only about 0.5 % to the cost of the active ingredient under the tested formulation conditions. That estimate does not prove commercial adoption, but it removes one common objection to complex nanoformulations: improved performance may arrive with impractical production costs.
A nanoscale formulation can work better for many reasons, and size is only one possible cause. By removing persistent carriers and surfactants, this study gives a clearer view of what nanosizing can do on its own. It improved target bioactivity, local plant uptake, and soil behavior without increasing measured toxicity in the tested nontarget organisms.
The result is not a universal recipe for better pesticides. Smaller particles help when the limiting barrier involves dispersion, adsorption, spreading, or local penetration. Other barriers may require controlled release, stronger adhesion, altered charge, or targeted delivery. Related work using plant-virus nanoparticles to deliver pesticide molecules into soil shows why carrier systems still matter, even when this study usefully isolates what size can do on its own. The useful question is no longer whether nano is better, but which barrier the nanoscale is being asked to solve.
For authors and communications departmentsclick to open
Lay summary
Prefilled posts
Nanowerk Newsletter
Get our Nanotechnology Spotlight updates to your inbox!
Thank you!
You have successfully joined our subscriber list.
Become a Spotlight guest author! Join our large and growing group of guest contributors. Have you just published a scientific paper or have other exciting developments to share with the nanotechnology community? Here is how to publish on nanowerk.com.
