Biological activity of 1,8 cineole, a major component of essential oil of Ocimum kenyense (Ayobangira) against stored product beetles

The efficacy of 1,8 cineole as repellent, toxicant and grain protectant against Sitophilus granarius, S. zeamais, Tribolium castaneum and Prostephanus truncatus was investiaged in the laboratory using contact toxicity, grain treatment and repellency assays. 1,8 cineole applied topically or imprenated on filter paper, whole wheat as well as maize grains was highly toxic to all the four beetle species. Beetle mortality was dose-dependent with the highest dose of 10 mu l/insect evoking 100% mortalities in the beetles after 24 h exposure. 1,8 cineole was more toxic in grain than on filter paper since the lowest dosage of 0.5 mu l/kg controlled all beetles exposed. There was, however, a highly significant loss of toxicity after only 24 h following treatment, irrespective of dosage applied. Development of eggs amd immature stages within grain kernels as well as progeny emergence were completely inhibited in treated grain. 1,8 cineole evoked strong repellent action against S. granarius and S. zeamais but was moderately repellent to T. castanum and P. truncatus. The protectant potential of products derived from O. kenyense against insect damage in traditional grain storage in Africa is discussed.