Repellence effectiveness of essential oils from some Tanzanian Ocimum and Hyptis plant species against afro-tropical vectors of malaria and lymphatic filariasis
Essential oils from three plant species growing in Dar es Salaam, Tanzania, Ocimum gratissimum (OG), Ocimum tenuiflorum (OT) and Hyptis suaveolens (HS) all from family Labiateae, were extracted by hydrodistillation and evaluated for laboratory and field based repellency against afro-tropical vectors of malaria and lymphatic filariasis. All oils were found to exhibit high mosquito repellency activity against Anopheles gambiae sensu stricto in the laboratory tests with RC50 values ranging from 2.0- to 15-×10?5 mg cm?2, whereas standard N,N-diethyl- 3-toluamide (DEET) was more repelling with RC50 value of 0.1×10?5 mg cm?2. The formulation containing 10% of O. gratissimum provided protection against mosquito bites from Anopheles funestus of 70.5 to 95.7%, A. gambiae of 63.2 to 91.5% and Culex quinquefasciatus of 83.8 to 89.5%. The 30% O. gratissimum formulation was more effective with better protection against mosquito bites from A. funestus of 84.2 to 96.6%, A. gambiae of 73.7 to 91.5% and C. quinquefasciatus of 89.5 to 91.5%. The formulation containing 15% DEET showed slightly lower protection against mosquito bites from A. funestus of 70.5 to 78.9%, A. gambiae of 68.4 to 94.0%, C. quinquefasciatus of 85.5 to 89.5% (P<0.05). The individual components of the oils were identified by GC-MS. The implication of these results in the development and promotion of repellent plant extracts for commercialization is of priority in rural Tanzania where whole plants are currently used as repellents against mosquito vectors.