Sylvia Mmbone, Margaret Mulaa, F.M Wanjala, Robert W.Nyukuri1 and Evelyn Cheramgoi
Efforts in research are focused on the bioactivity, application methods, cost-effectiveness and sustainable use of botanical pesticides against insect pests. The insecticidal and repellent properties of Tagetes minuta L (Mexican marigold) and Tephrosia vogelii Hook (Fish poison bean) collected from KARI, Kitale botanical garden were evaluated for their efficacy and repellence against red spider mite (Tetranychus urticae Koch) and black bean aphids (Aphis fabae Scopoli) in the laboratory. Mortality potential of the plant was determined by spraying the crude extracts on the pests reared earlier in the screen house. Tagetes minuta crude extracts at concentrations of 50 g/L, 100 g/L, 150 g/L soaked for 24 hours and also 150 g/L soaked 48 hours in distilled water, Tephrosia vogelii crude leaf extract of 10 g/L, 30 g/L and 60 g/L soaked 12 hours and also 60 g/L soaked 48 hours in distilled water, were used to investigate treatment efficacy on mortality of the adult insects. Treatment using T.minuta at concentration 150 g/L soaked for 48 hours caused the highest mortality in aphids with R2=0.9908 and slightly lower mortality in mites with R2= 0.9505. T. vogelii at concentration 60 g/L soaked 48 hours in water caused high mortality in the two pests with R2=0.9826 in aphids and R2=0.9767 in mites at the end of 24 hour exposure to the herb. Repellency tests were performed using filter- paper circles and extracts of T.minuta and T. vogelii were applied around the periphery of the filter papers. Percentage repellency (PR) was determined for each extract. T.minuta at concentration 150 g/L soaked 48 hours had the strongest PR on mites at 55% followed by that soaked 24 hours PR at 12%. T. vogelii at 60 g/L soaked 48 hours had a moderate repellent effect on mites at PR 17% while same concentration after 12 hours of soaking had PR of 8% on mites. However aphids were not repelled by any of the extracts used. The two botanicals are promising insecticides which can be used by subsistence farmers as alternatives to synthetic pesticides.
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