D3332: Repellency and toxicity of thymol based synthetic derivatives against imported fire ants

Imported fire ants are considered one of the most serious medical and agricultural pests across the globe. They mainly include Solenopsis invicta Buren (Red Imported Fire Ant), Solenopsis richteri Forel (Black Imported Fire Ant), and the hybrid of these species (S. invicta x S. richteri). As part of the identification of potential fire ant control agents, a series of plant essential oil-derived terpenoid compounds were screened. Amongst them, thymol and carvacrol demonstrated potent repellent effects and moderate toxicities against the aforementioned three fire ant species. Using these molecules as templates, a set of derivatives were prepared, incorporating various ester and carbamate functionalities. In the biological screening (fire ant repellency experiment and contact toxicity assay), the developed molecules demonstrated comparable potential than the parent molecules. Furthermore, based on the obtained biological experimental data, a preliminary structure-activity relationship was deduced which suggested the importance of these chemical modifications. The repellency activity observed was corroborated with molecular docking of the compounds with the pheromone-binding protein GP-9 (Source: Solenopsis invicta x Solenopsis richteri). Site mapping predicted the putative binding sites. The screened compounds gave comparable docking scores. Overall, these findings highlight the potential role of thymol-derived products in fire ant management and further structural optimization might be helpful for the development of commercial fire ant control products.