Repellency of carvacrol, thymol, and their acetates against imported fire ants

Authors: PAUDEL, PRADEEP - University Of Mississippi; SHAH, FARHAN - University Of Mississippi; GUDDETI, DILEEP - University Of Mississippi; ALI, ABBAS - University Of Mississippi; Chen, Jian; KHAN, IKHLAS - University Of Mississippi; LI, XING-CONG - University Of Mississippi

Submitted to: Insects
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/24/2023
Publication Date: 9/28/2023
Citation: Paudel, P., Shah, F.M., Guddeti, D.K., Ali, A., Chen, J., Khan, I.A., Li, X. 2023. Repellency of carvacrol, thymol, and their acetates against imported fire ants. Insects. 14(10):790. https://doi.org/10.3390/insects14100790.
DOI: https://doi.org/10.3390/insects14100790

Interpretive Summary: Fire ants are a significant pest and their control heavily relies on synthetic insecticides. The extensive use of insecticides has led to the public concern on their potential negative effects on human health and the well-being of wildlife and environment. Repellants are useful in managing fire ants, for example, repellants can be used to prevent fire ants from invading sensitive areas, such as electrical equipment, nursing homes, and hospitals. Particularly the plant-derived natural repellants may provide a safer and more environmentally friendly alternative. This study investigates the repellency of essential oil-derived compounds, carvacrol, thymol, and their acetate against imported fire ant workers. The results revealed that carvacrol was the most potent repellent against imported fire ants. Thymol also exhibited strong repellency. Furthermore, thyme-red essential oil, characterized by a thymol chemotype, was found to effectively repel fire ants. In contrast, thyme essential oil, characterized by a linalool chemotype lacking thymol and carvacrol, did not exhibit any repellent effect. This study provides the first evidence of the potent repellency of carvacrol and thymol against imported fire ant workers, indicating their potential as promising repellents for fire ant control.

Technical Abstract: In the United States, imported fire ants are commonly referred to as the red imported fire ants (Solenopsis invicta Buren), black imported fire ants (S. richteri Forel), and the hybrid imported fire ants (S. invicta × S. richteri). They are significant pests, and their control heavily relies on synthetic insecticides. The extensive use of insecticides has led to the public concern on their potential negative effects on human health and the well-being of wildlife and environment. As an alternative, plant-derived natural compounds, particularly essential oils (EOs) and their main constituents, show promise as safer and environmentally friendly products for controlling fire ants. Repellants are useful in managing fire ants and the plant-derived natural repellants may serve as a safer and more environmentally option. This study investigates the repellency of EO-derived compounds, carvacrol, thymol, and their acetate against imported fire ant workers. The results revealed that carvacrol, a GRAS compound (Generally Recognized As Safe), was the most potent repellent against S. invicta, S. richteri, and their hybrid with a minimum repellent effective dose (MRED) of 0.98 µg/g, 7.80 µg/g, and 0.98 µg/g, respectively. Thymol also exhibited strong repellency, with MREDs of 31.25 µg/g, 31.25 µg/g, and 7.8 µg/g, respectively. Furthermore, thyme-red essential oil, characterized by a thymol chemotype, containing 48.8% thymol and 5.1% carvacrol, was found to effectively repel the hybrid with an MRED of 15.6 µg/g. In contrast, thyme essential oil, characterized by a linalool chemotype lacking thymol and carvacrol, did not exhibit any repellent effect, even at the highest test dose of 125 µg/g. This study provides the first evidence of the potent repellency of carvacrol and thymol against imported fire ant workers, indicating their potential as promising repellents for fire ant control.