Oregano Oil Shows Promise as Natural Fire Ant Repellant

A new study from the University of Mississippi suggests that an herb commonly used in Italian cooking may hold the answer.

A team of researchers at the UM National Center for Natural Products Research have discovered that essential oils from oregano may offer an effective, nontoxic way to control the stinging invasive insects.

Xing-Cong Li, a principal scientist at the natural products center and research professor of pharmacognosy at the School of Pharmacy, is a co-author of the study published in Pest Management Science.

"Our study shows that a natural compound safe enough to flavor food can also manage one of the world's most aggressive invasive species," Li said. "By understanding the chemistry behind these natural repellents, we can develop pest control solutions that are both effective and environmentally safe." 

The repellent effects of the essential oils from oregano have not been tested on humans yet.

Fire ants are among the most damaging invasive species of ants found in America. They first entered the country through the port of Mobile, Alabama, and have spread across the southern U.S. from the Atlantic Coast to California.

Imported fire ants have invaded about 350 million acres in the U.S., and they cause some $8 billion in economic damages per year, including damage to livestock and other agriculture, according to the National Invasive Species Information Center in the U.S. Department of Agriculture.

The natural products center has an ongoing program to find safer alternatives to synthetic pesticides to control fire ants. After determining that oregano essential oil has potential to repel imported fire ants, the Ole Miss scientists analyzed the oil's chemical makeup and discovered that one compound, called carvacrol, is responsible for its strong repellent effect.

To learn more, the team tested 21 similar compounds, either purchased or made in the lab, to see which ones worked best.

Finally, they used computer modeling to see how these compounds might interfere with the ants' ability to detect pheromones, the chemical signals they use to communicate.

"Carvacrol and its analogs could serve as the basis for new, plant-derived repellents suitable for gardens, farms and even home use," Li said. "Since carvacrol is already recognized as safe by the U.S. Food and Drug Administration, it holds strong potential for real-world applications in sustainable pest management."

Besides causing agricultural and property damage, fire ants pose a health hazard for humans. The ants sting thousands of people each year, causing painful, burning rashes and allergic reactions in sensitive individuals.

Plant-derived compounds such as carvacrol are biodegradable and generally less toxic to people, pets and beneficial insects, said Abbas Ali, a principal scientist at NCNPR and a co-author of the study. This approach supports sustainable agriculture and safer pest management by reducing dependence on synthetic and potentially harmful chemicals, he said.

"The products we're developing act as repellents – what we call digging suppressants in fire ants," Ali said. "These prevent fire ants from digging to form nests. For example, when you treat an area with a digging suppressant, the ants can't dig to build a nest.

"We're particularly focused on natural products. While some don't cause high mortality, they're still very effective for population management. The goal is to either drive the ants away from sensitive areas or develop treatments that combine repellency and mortality – so they both kill the ants and prevent them from digging or nesting in the soil."

Ali has studied a variety of natural products for years, searching for alternative to synthetic chemicals.

"As a researcher, I think this is an area that's been lacking in fire ant research overall," he said. "Even when a product is available, it's important to know how to properly apply or position it in the field to achieve effective control, and that's what we're studying."

This research was funded by the U.S. Department of Agriculture – Agricultural Research Service under grant nos. 58-6066-6-043 and 58-6066-1-025.

Top: Scientists at the National Center for Natural Products have found that carvacrol, a compound found in oregano oil, naturally repels invasive fire ants. The discovery opens the door to a potentially safer alternative to chemical pesticides. Photo illustration by Stefanie Goodwiller/University Marketing and Communications