Background
Plant oils possess biological activities which offer tremendous potential for disease vector management. This study investigated the bioactivity of selected insecticidal plant oils against Anopheles gambiae s.s. Kisumu Susceptible Strain (KSS) mosquitoes. The plant oils from leaves of Hyptis suaveolens, Ocimum gratissimum, Nicotiana tabacum, Ageratum conyzoides and fruit peels of Citrus sinensis were extracted and the major chemical components analysed using coupled gas chromatography-mass spectrometry (GC-MS). The spatial toxicity effects of the plant oils were tested at different concentration (0.1 mg/ml, 0.3 mg/ml and 0.5 mg/ml) against An. gambiae s.s. KSS in a Peet-Grady Chamber. Deltamethrin was used as the positive control.
Results
D-Limonene was the major chemical component found in Ci. sinensis and Ni. tabacum. Prococene I was the major chemical component in Oc. gratissimum while P-Xylene had the highest percent composition in Ni. tabacum. The control (Deltamethrin) and 0.3 mg/ml concentration of oil from Oc. gratissimum elicited a 100% knockdown on An. gambiae s.s. KSS. At 0.5 mg/ml, oils from Ci. sinensis, Oc. gratissimum and Ni. tabacum elicited significantly (P > 0.05) the same knockdown effect (100%) as the control on An. gambiae s.s. KSS. After 24hrs post-exposure, all the plant oils evaluated elicited 100% mortality on An. gambiae s.s. KSS at both 0.3 and 0.5 mg/ml. The lowest knockdown times KdT50 (34.80 minutes) and KdT95 (92.50 mins) were noted at the lowest concentration (0.1 mg/ml) of oils from Ni. tabacum which was better compared to the control (36.1 and114.9 mins respectively) against An. gambiae s.s. KSS.
Conclusions
Oc. gratissimum and Ni. tabacum displayed excellent spatial toxicity capabilities against An. gambiae s.s. KSS and can be incorporated into the management of malaria vectors in Nigeria.