Researchers at Kyushu University have developed a plant-based insecticide by processing compounds from garlic and spearmint into oil-in-water nanoemulsions. The study, published in Ecotoxicology and Environmental Safety, tested the formulation against the adzuki bean beetle, a pest that causes significant postharvest losses in stored legumes.
The team used ultrasonication to create droplets of 50–60 nanometers from diallyl disulfide (DDS), an organosulfur compound from garlic, and R-carvone (Car), a monoterpenoid from spearmint. Compared with the raw compounds, the nanoemulsions increased beetle toxicity by 30.5% for DDS and 8.2% for Car, and a mixture of the two further enhanced the effect.
In tests on a non-target species, the parasitic wasp Anisopteromalus calandrae — a natural enemy of the beetle — showed relatively low mortality. When the nanoemulsion killed half the beetles, no more than 22% of the wasps died, suggesting the formulation could be combined with biological control.
The nanoemulsions also proved safe for adzuki seeds; no residual compounds were detected on the seeds, and root growth was enhanced. The researchers say the absence of residues supports potential use in food storage.
Next steps include verifying efficacy under real-world storage conditions and at larger scales, as well as investigating the mechanism behind the beetle's reduced lifespan. The team also plans to test the nanoemulsion on other pests with a view toward commercialization.
Lead researcher Professor Midori Tuda said the goal is a sustainable, environmentally friendly alternative to synthetic insecticides. First author Urvashi Sahu noted that plants have evolved potent defensive compounds, and nanotechnology can amplify their practical utility.
Natural insecticide made from compound found in garlic and spearmint kills bean beetles effectively
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