Fruit flies Bactrocera dorsalis (Diptera: Tephritidae) are major pests of various horticultural products. They present in many countries and particularly in tropical and subtropical regions [1] [2] [3] [4] [5] . This fruit fly is a major pest of mango in Senegal. Agricultural production losses due to this fly are the basis of a reduction in exports, of an increase in and of quarantine services [4] [6] [7] . In Senegal, fruit fly attacks cause yield losses of around 30% to 60% depending on the area [6] .

Several strategies are used to combat fruit flies, such as collecting infested fruits (sanitation) [8] [9] [10] , spraying insecticide or protein baits [11] [12] , trapping with attractants [13] [14] , the release of natural enemies [15] [16] and the sterile insect technique [17] . However, pesticides endanger the health and well-being of farmers and consumers. They also cause serious damage to the environment [2] [3] . It is therefore essential to find alternative and environmentally friendly management techniques to combat these fruit flies. The current trend is moving towards the use of natural plant-based products for more sustainable control. Many studies have shown that essential oils can be used to control fruit flies. It has been reported that essential oils of Syzygium aromaticum [2] , Melaleuca bracteata [3] , Ocimum sp. rich in methyleugenol (64.2% - 73.5%) [3] [18] and Myristica fragrans containing 8.33% methyleugenol [19] have the ability to attract male fruit flies. However, in Indonesia, the repellent activity of Pogostemon cablin essential oil against B. dorsalis has been reported [20] . Thongdon et al. (2009) showed that Limnophila geoffrayi oil rich in d-Pulegone (27.1%) and perillaldehyde (19.1%) has significant insecticidal properties against B. dorsalis flies [21] .

In Senegal and Gambia, the leaves of Ocimum americanum, also known as Oimum canum, have been used for several years to control B. dorsalis. However, to our knowledge, no chemical studies have been performed to support this practice. Thus, the aim of this study was to determine the chemical composition of oils from the leaves of O. americanum collected in these two neighboring countries.

The essential oil yields from O. americanum leaves harvested in Senegal and Gambia were 3.84% and 2.13%, respectively. These yields are similar to those reported in Brazil (3.6%) [26] and Kenya (4.0%) [27] . On the other hand, they are very high compared to others described in the literature (8% - 9%), in Benin and Kumaun Himalayas [28] [29] [30] [31] . The analysis of the leaf essential oils by GC/FID and GC/MS allowed the identification of 23 compounds representing almost 100% of the total compositions (Table 1). These essential oils were mainly dominated by methyleugenol (72.0% and 75.8%, respectively). The other components in significant percent were trans-β-caryophyllene (13.9% and 13.0%, respectively), germacrene D (4.1% and 3.7%, respectively), β-elemene (3.3% and 0.9%, respectively). These results show that the two samples collected in these two neighbouring countries have virtually the same chemical composition. This confirms that the same plant is used in both countries to combat fruit flies.

However, several research works aimed at expanding knowledge about the essential oil of O. americanum, reveal that the chemical composition of the oil varies according to the geographical origin. To our knowledge, we report for the first time such a high content of methyleugenol in the essential oil of O. americanum. In this plant species, the highest content of methyleugenol (14.8%) known so far in the literature was reported by, Singh et al. (2013) for samples harvested in the Himalayas [32] . In other studies, methyleugenol was present at lower concentrations (trace-7.5%). However, most chemotypes of this species are dominated by compounds derived from the phenylpropanoid: thymol/p-cymène/ γ-terpinene [26] ; eugenol/δ-cadinene [33] ; eugenol/ (E)-caryophyllene/methyleugenol [32] ; eugenol/methylchavicol [32] [34] ; methylchavicol/linalool [32] ; methylchavicol/eugenol [32] [35] ; transmethylcinamate [36] . In some studies, terpenes were described as the main constituents: terpineol, linalol, neral, geranial, terpinen-4-ol, γ-terpinene, camphor, longipinol, 1,8-cineole, β-bisabolene, limnene, γ-salinene, carvotanacetol and carvacrol [27] [28] [29] [31] [35] - [47] . This chemical variability may be due to climatic conditions, soil conditions and genetic mutations.

This study reported the chemical composition of the essential oils of O. americanum from Senegal and Gambia. These essential oils are mainly dominated by methyleugenol. As for other plant species rich in methyleugenol, we plan to evaluate the attractive effect of the essential oil and the powder of the leaves of O. americanum against B. dorsalis, which is a real pest of mango orchards in Senegal.

We thank the SyRIMAO/ECOWAS Project for its financial and technical support.

The authors declare that there is no conflict of interest related to this article.

Tine, Y., Sinzogan, A.A.C., Ndiaye, O., Sambou, C., Diallo, A., Mbenga, I., Badji, K., Dieng, E.H.O., Balayara, A., Diatta, J., Gaye, C., Paolini, J., Costa, J., Wele, A. and Ngom, S. (2024) The Essential Oil of Ocimum americanum from Senegal and Gambia as a Source of Methyleugenol for the Control of Bactrocera dorsalis, Fruit Fly. Journal of Agricultural Chemistry and Environment, 13, 133-141. https://doi.org/10.4236/jacen.2024.131009