Repellency of oregano (Lamiales: Lamiaceae) essential oil against Bactrocera dorsalis (Diptera: Tephritidae): active ingredients, electroantennographic responses, and an orchard cage assay

The oriental fruit fly, Bactrocera dorsalis (Hendel) (Diptera: Tephritidae), is a devastating pest of global fruit production. Current control methods largely rely on methyl eugenol, which targets males, leaving a management gap since females cause direct crop damage through oviposition. This study investigated twelve plant essential oils and identified oregano (Origanum vulgare L.) essential oil (EO) as the most effective repellent and oviposition deterrent. Oregano EO demonstrated the strongest repellent activity in Y-tube olfactometer assays, with an EC50 value of 49.64 μl/ml. Carvacrol and thymol were identified as the active ingredients. In orchard cage assays, all 3 compounds exhibited significant oviposition deterrence (over 70% at 20 μl/ml within 24 h), with no significant differences among them. Persistence assays showed that oregano EO maintained significantly higher deterrence than carvacrol and thymol during days 1 to 6. Electroantennography revealed that at 50 μl/ml, oregano EO, carvacrol, and thymol elicited response values of 6.47, 6.48, and 7.01, respectively. These results demonstrate that oregano EO, carvacrol, and thymol are effective repellents and oviposition deterrents for B. dorsalis, which can be deployed in strategies targeting the crop damaging female population. This work provides a foundation for developing female focused behavioral management tools in sustainable fruit pest control.