Larvicidal, Ovicidal and Repellent Activities of Leucas stachydiformis (Hochst. ex Benth.) Briq Essential Oil against Anopheles arabiensis

Abstract

Background: Despite tremendous efforts made to curb malaria morbidity and mortality, malaria control has slowed down due to resistance to all currently used insecticides by mosquitoes, and their negative effect on the non-target organisms and the ecosystem. Thus, there is an urgent need to search and develop new plant-based malaria vector control strategy from medicinal plants origin such as essential oil. Methods: Larvicidal effect was tested against the fourth instar An. arabiensis wild larvae whilst freshly laid ova of An. arabiensis were used to determine ovicidal activity of the essential oil at concentrations ranging from 6.25 to 400 ppm. Concentrations of 41.6–366.7 µg/cm2 were used to evaluate repellent activity of the essential oil on 3–5 days old adult female An. Arabiensis. The essential oil composition of Leucas stachydiformis was also analyzed using GC-MS. Results: Larvicidal, ovicidal and repellent activities of the essential oil extracted by hydrodistillation from leaves of the endemic Ethiopian plant Leucas stachydiformis (Hochst. ex Benth.) Briq was investigated against Anopheles arabiensis, the dominant malaria vector species in Ethiopia. The study revealed that the oil possesses the highest larvicidal activity at 400 ppm and 200 ppm after 24 h and 48 h treatment. LC50 values for the fourth larval instar after 24 h and 48 h treatment were 43.4 ppm and 34.2 ppm, respectively. After 72 h exposure, the oil displayed 100% ovicidal activity at 400 ppm with IH50 value of 32.2 ppm. In the repellency test, at concentrations of 366.7, 133.3 and 41.6 µg/cm2, the oil gave total percentage protection of 67.9 ± 4.2%, 37.2 ± 2.8% and 32 ± 2.2%, respectively, for 4 hours. The highest concentration (366.7 µg/cm2) gave 100% protection up to 90 min. GC-MS analyses of the oil revealed the presence of 24 compounds representing 90.34% of the total oil with caryophyllene oxide, germacrene D, and trans-caryophyllene constituting more than 50% of its components. Conclusion: Results of the present study suggest that the essential oil of L. stachydiformis has the potential to be used for the control of An. arabiensis mosquitos.