EFFECTS OF ESSENTIAL OILS OF Lantana camara AND TWO OCIMUM SPECIES ON BEAN WEEVIL (Acanthoscelides obtectus) AND THEIR CHEMICAL COMPOSITIONS

Crude plant products have been widely used by different communities in Africa for pest control. Synthetic insecticides have a number of drawbacks, such as development of genetic resistance, eco-toxicity, negative health effects to users and high cost of application. However, not enough scientific research has been conducted on the efficacy of traditional methods in weevil control, the chemical profiles of plant products and their safety to the users. The bioactivities of the powedered products and essential oils of three plants, namely Ocimum gratissimum, Ocimum americanum and Lantana camara, growing in Eastern Kenya against common bean weevil (Acanthoscelides obtectus) were determined. Actellic Super and untreated bean grains were used as positive and negative control, respectively. The powdered plant materials (dried leaves) induced relatively low mortality, with the most effective.

 americanum (Kitui) causing 52% mortality at dose level of 30% w/w after 28 days. The essential oils of all the three plants were found to have significant repellency to the bruchid. The most repellent essential oil was that of L. camara (Kitui) (RD50 0.26 µl per cm ), followed by O. gratissimum (Kitui) (RD50 0.33 µl per cm ), then O. americanum
(Kitui) (RD50 0.44 µl per cm ). However, the repellencies of the essential oils of the same species of plants from Machakos region were lower [L. camara (Machakos) RD50 0.62 µl per cm ; O. americanum (Machakos) RD50 0.75 µl per cm and O. gratissimum (Machakos) RD50 0.92µl per cm ]. The essential oils of the three plants also showed significant mortality, with LD50 of that of O. americanum (Kitui) being 5.28µl per cm , that of O. gratissimum (Kitui) being 5.39 µl per cm and that of L. camara (Kitui), 14.55 µl per cm . The essential oils of the plants from Machakos region gave  the following mortalities: O. americanum (Machakos) LD50 34.20 µl per cm , O. gratissimum (Machakos) LD50 89.93 µl per cm
and L. camara (Machakos) LD50 19.48 µl per cm . The oil from O. americanum (Kitui) gave the best mortality