EFFICACY OF Tagetes minuta L AND Tephrosia vogelii Hook CRUDE LEAF EXTRACTS ON Tetranychus urticae Koch AND Aphis fabae Scopoli

Abstract

Red spider mites and aphids are examples of agricultural pests which are very problematic to many farmers in Kenya and further Sub- Saharan Africa. Efforts research wise 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 and Tephrosia vogelii Hook collected from KARI, Kitale botanical garden were evaluated for their efficacy and repellence against red spider mite Tetranychus urticae Koch and aphids Aphis fabae Scopoli of broad beans (Vicia faba) in the laboratory and in the field. Mortality potential of the two plants was determined by spraying the crude extracts on the insects. 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; 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, synthetic insecticides (Alpha cymba 10 EC for aphids and Disect for mites) were used to investigate treatment efficacy on mortality of the adult insects. Tetranychus urticae and Aphis fabae were artificially infested in the screen house on potted bean plants placed on a bench in a screen house at KARI Kitale. Treatment using T.minuta at concentration 150 g/L soaked for 48 hours caused a percent mortality of 90% in aphids and 69% in mites, while same concentration at 24 hour soaking caused percent mortality of 84% in aphids and 35% in mites. T. vogelii at concentration 60 g/l soaked 48 hours in water caused percent mortality of 98% in aphids and 92% in mites at the end of 24 hour exposure to the herb. The same concentration at 12 hour soaking caused percent mortality of 94% in aphids and 60% in mites. Repellency tests were performed using filter- paper circles on mites and aphids. The 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.