Background: Citrus limon seeds have limited exploration, compared to other parts. The increasing prevalence of mosquito menace prompted the investigation into the repellent effects of the seed n-hexane extract and fractions of Citrus limon (Rutaceae) against adult Anopheles gambiae sl mosquitoes. The cytotoxicity and chemical constituents of the 100% n-Hexane Fraction (HF) were also evaluated.

Methods: Successive extraction was done with cold-maceration using, n-hexane, Ethyl Acetate (EA) and methanol. The three solvent extracts were screened against Anopheles gambiae sl mosquitos, using human bait method, at doses, 1.5, 2.5 and 5.0 mg/ml and with Deet and acetone used as positive and negative controls respectively. The n-hexane extract was further fractionated with column chromatography. Ten fractions (100% n-hexane, 10, 20, 30, 40, 60, 80% EA in n-hexane, 100% EA, 50% methanol in EA, and 100% methanol) were collected, and all tested at a single optimized dose of 5 mg/ml for 2 hr. The cytotoxicity and the chemical constituents of HF were determined using brine shrimp lethality test and gas chromatography-mass spectrometry respectively.

Results: N-hexane extract and HF, both at 5 mg/ml, showed the most protective effect of 97.52 and 89.40% respectively, compared with standard (Odomos Deet) 100% activity, with no significant difference (p>0.05) between the three. HF was toxic with LC₅₀ values of 29.2354 ppm. Thirty compounds representing 79.25% of HF were identified. Major compounds present in the fraction were heptadecanamine (8.31%), N-(3-methylbutyl) acetamide (7.89%), 2-ethyl- 1-hexanamine (6.65%).

Conclusion: This promising repellent activity further justified the traditional usage of Citrus limon as mosquito repellent.