Investigation on chemical composition and insecticidal activity against Anopheles gambiae of essential oil obtained by co-distillation of Cymbopogon citratus and Hyptis suaveolens from Western Burkina Faso

Abstract

Background: Essential oils of Cymbopogon citratus and Hyptis suaveolens are known for their insecticidal properties, but remain ineffective against mosquitoes resistant to synthetic insecticides. In order to improve insecticidal properties of these plants, this study aimed to investigate the chemical composition and insecticidal activity against Anopheles gambiae mosquitoes of essential oil obtained by co-distillation of dry leaves of C. citratus and H. suaveolens.

Methods: Essential oils were extracted by hydrodistillation from dry leaves of C. citratus and H. suaveolens, separately, then from the mixture of the dry leaves of the two plants in mass ratio 50/50. Each pure essential oil and the mixture obtained either by co-distillation or by combining pure essential oils in volume ratio 50/50 were then analysed by GC/MS. All essential oils and Deltamethrin 0.05% (positive control) were tested on two species of mosquitoes of the genus Anopheles gambiae according to the World Health Organization standard methods.

Results: Essential oil obtained by co-distillation mainly contained piperitone (40.80%), 1,8-cineole (24.64%), p-menth-4(8)-ene (13.20%), limonene (6.09%) and α-pinene (4.73%). However, the mixture of pure essential oils of these two plants mostly contained geranial (20.74%), neral (16.42%), 1,8-cineole (19.79%), sabinene (6.03%) and β-pinene (3.87%). The essential oil of C. citratus mainly contained geranial (41.49%), neral (32.83%), β-myrcene (13.66%) and geraniol (3.49%) while the major constituents of essential oil of H. suaveolens were 1,8-cineole (39.58%), sabinene (12.06%), β-pinene (7.73%), α-terpinolene (6.72%) and (E)-caryophyllene (7.49%). At the dose of 1%, all essential oils, except that of H. suaveolens, induced about 100% of mortality on the sensitive species of An. gambiae. However, on the resistant species at the same dose, the essential oil obtained by co-distillation induced the highest mortality (53.44%). The essential oils of C. citratus, H. suaveolens and the mixture of the two pure essential oils caused respectively 2.47, 15.28 and 18.33% of mortality. The synthetic insecticide caused 100 and 14.84% of mortality respectively on the sensitive and resistant species of An. gambiae.

Conclusion: Essential oil obtained by co-distillation showed good insecticidal efficacy against a resistant species of An. gambiae and might constitute a new solution to fight against mosquitoes resistant to synthetic insecticides.

Keywords: Cymbopogon citratus; Hyptis suaveolens; Co-distillation; Essential oil; Insecticidal activity; Resistant Anopheles gambiae.

Fig. 1

Structures of main constituents of essential oil of C. citratus (a), H. suaveolens (b) essential oils and that obtained by co-distillation of the two plants (c)

Fig. 2

Mortality rate caused by essential oils on sensitive (A) and resistant (B) species. CC essential oil of C. citratus, HS essential oil of H. suaveolens, CC/HS essential oil obtained by co-distillation of the two plants, CC/HS* mixture obtained by combining pure essential oil, Delta 0.05% Deltamethrin 0.05%. The bands assigned the same letter are not significantly different according to the Student-Newman and Keuls test at the 5% threshold

Fig. 3

Probable mechanism of piperitone formation from neral and geranial

Fig. 4

Probable mechanism of p-menth-(4)8-ene formation from sabinene

Fig. 5

Probable mechanism of d-limonene formation from myrcene and β-pinene