Larvicidal Activities of the Leaves of Eugenia uniflora L. (Myrtaceae)

Eugenia uniflora L. (Myrtaceae) leaves are used ethnomedicinally in Nigeria for diseases such as malaria and in Brazil they are spread on the floor for their insect-repellent activity. Continued search for plant larvicides useful in the control of vector of Dengue fever compelled bioactivity guided fractionation of E. uniflora leaf for lethality against fourth instars larvae of Aedes aegypti. The active methanolic extract (A) had larvicidal activity (LC₅₀ 2.74 and 2.18 mg/ml at 24 and 48h) that was comparable (p > 0.05) to Endosulphan (LC₅₀ 0.93 and 0.90 mg/ml at 24 and 48h). The n-hexane partition fraction (B ₁) with similar activity (LC₅₀ 2.58 and 1.87 mg/ml at 24 and 48h) was the most active partition fraction and should contain the larvicidal constituents. Vacuum liquid chromatography of B ₁ and eluting with n-hexane, chloroform and methanol mixtures gave fifth and sixth bulked fractions (C ₅ & C ₆) with significantly (p < 0.05) higher larvicidal activities. Column chromatography of the combined C ₅ & C ₆, similary eluted as above, yielded 1^st and 3^rd subfractions (D ₁ & D ₃) with LC₅₀ 1.01 and 1.17 mg/ml at 24h, respectively and activities that were similar ('p > 0.05) to that of Endosulphan and better than those of C ₅ & C ₆, only at 24h. Activities of the D ₁ – D ₄ subfractions at 48h were comparable with those of the mother fractions (C ₅ & C ₆), and Endosulphan. The results established the larvicidal activity of E. uniflora leaf and identified D ₁ & D ₃ as the most active subfractions that could be further developed as alternative larvicides in the control of Dengue fever, especially among the rural populations of Africa.

Fig. 1: Larvicidal activities of Eugenia uniflora extract and fractions against Aedes aegypti at 24 hr.A: methanolic extract; B₁: n-hexane fraction; C₅: VLC fraction; C₆: VLC fraction; D₁: column fraction; D₃: column fraction; ENDO: Endosulphan (positive control). The larvicidal activities of the extracts and fractions were compared with that of Endosulphan (positive control) using one way analysis of variance (ANOVA) followed by Bonferonni post-hoc test. *: p < 0.05 significantly different from Endosulphan. N = 6.