Lippia javanica (Burm F) Spreng: its general constituents and bioactivity on mosquitoes.

Mosquito repellent plants are used in the rural areas of Zimbabwe despite the fact that very few of them have been biologically evaluated. Leaves of the plant Lippia javanica, were collected from Mumurwi village, Zimbabwe and evaluated for repellency against laboratory reared Aedes aegypti mosquitoes. Major plant compounds were identified using Thin Layer Chromatography (TLC) and Mass Spectrometry (MS). Fraction 'A' contained coumarins, flavonoids and essential oils and offered a protection time of 8 and 5.5hrs in choice and non-choice experiments respectively. Fraction 'B1' contained flavonoids with a protection time of 1 and 0.5hrs in choice and non choice experiments respectively. Fraction 'B2' contained coumarins and essential oils and offered a protection time of 2hrs in either test. No major compounds were identified from the following fractions: 'C1', 'C2', 'D1', 'E1', 'E2', 'F1' and 'F2' and all of them failed to give 100% repellence. The 'C1' supernatant fraction contained coumarins and provided protection from mosquito bites for 1 and 0.5 hrs in choice and non-choice experiments respectively. Fraction 'C2' did not have the major compounds but gave a protection time of 1 hr in either experiment. Fraction 'D2' contained essential oils only and it provided a protection time of 2.5hrs in choice experiments. Analysis by MS showed the presence of alpha pinene, 1,3-5 cycloheptatriene, beta phellandrene, (+)-2-carene, 3-carene, eucalyptol and caryophyllene oxide. L. javanica offered protection from mosquito bites for 8hrs (choice) and 5.5hrs (non choice experiments). The combined presence of coumarins, flavonoids and essential oils have an additive effect compared with individual plant fractions.