Evaluation of Ocimum kenyense (Ayobangira) as source of repellents, toxicants and protectants in storage against three major stored product insect pests

The bioactivity of materials derived from the leaves and succulent stems of Ocimum kenyense against Sitophilus zeamais (Mots.), Rhyzopertha dominica (Fab.) and Sitotroga cerealella (Oliv.) was assessed in maize and sorghum grains in the laboratory. O. kenyense applied as dry or ground leaves was not toxic to S. zeamais and R. dominica. The highest dosage of essential oil killed only 35% of the weevil but induced 96% mortality in the borer after 96 h. S. cerealella was most susceptible to O. kenyense since all the plant materials bioassayed evoked higher mortalities in the moth. Grains treated with 30 g of ground leaves and 750 mg of essential oil killed all the moths after 24 h. Similarly, dry and ground leaves had no effect on progeny production by S. zeamais but grains treated with essential oil extract significantly reduced the number of progeny produced by the weevil. All levels of dry leaves, ground leaves and essential oil extract of O. kenyense caused significant reduction in progeny produced by R. dominica and S. cerealella. There was no progeny produced by both species in grains treated with the highest dosages of 30 g of ground leaves and 750 mg of essential oil extract. All the plant materials were highly repellent to S. zeamais, with the highest dosages of ground leaves and essential oil evoking the highest repellent action. The materials, however, showed only moderate repellency against R. dominica and rather low repellency against the moth. Ground leaves and essential oil extract provided the greatest protection of maize and sorghum against feeding by R. dominica and S. cerealella with no observable feeding damage to grains treated the highest dosages of both materials. The potential practical use of O. ken?tense as grain protectants in farm-stored grains in rural communities in Africa is discussed.