Repellent activity of the essential oils of Cleome monophlla L., C. hirta Oliv, Gynadropsis gynandra Brig. and Capparis tomentosa Lam., and their chemical constituents against Sitophilus zeamais and Rhipicephalus appendiculatus
Ndung'u, Mary Wambui
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The essential oils of Cleome monophylla L., C. hirta Oliv. Gynandropsis gynandra Brig. and Capparis tomentosa Lam. were extracted by steam distillation. All the oils exhibited repellent activity against sitophilus zeamais and Rhipicephalus appendiculatus. The repellent activities were studied using the Y-shape olfactometer and the tick climbing bioassay methods for S. zeamais and R. appendiculatus, respectively. The oil content of each plant species is reported (percent yield). The refractive index, specific gravity and optical rotations of the C. monophlla, C. hirta and G. gynandra oils are reported. The analysis of the oils was carried out by GC and GC-MS methods. The compounds myrcene (0.7), terpinolene (1.4), -cubebene (0.4), 3-undecanone (3.1), (+) - humulene (9.2), 1--terpineol (15.0), 2-dodecanone 95.6), -ionone (1.1), (+) - cedrol (0.9), carvacrol (1.6), n - docosane (3.5), phytol (7.2), n-pentacosane (14.0) and n-octacosane (0.9) were identified from the oil of C. monophylla., (+)-Cedrol, phytol, pulegone, n-octacosane and 1-4-terpineol were identified from C. hirta oil. Linalool, geraniol, (+)-cedrol, n-docosane and phytol were identified from G. gynandra oil. All these compounds showed repellent activity against S. zeamais and R. appendiculatus. This bioassay activity showed that the oils and most of their constituents were more active than the synthetic standard, N, N-diethyl-m-toluamide (DEET) at various dose levels. In view of the activity of these oils and their constituents, it is suggested that these plants are suitable for the possible exploitation in pest control.