Determination of the appropriate doses of promising botanical powders against maize weevil, Sitophilus zeamais Mots (Coleoptera: Curculionidae) on maize grain

Abstract

The present laboratory study was carried out in the entomological laboratory the Department of plant science, Ambo University. The experiment was carried out using randomized complete block design with three replications to evaluate the efficacy of four locally available botanicals. The botanicals evaluated were: Neem (Azadirachta indica) leaf and seed, hop bush (Dodonae angustifolia) fresh leaf, Pyrethrum (Chrysanthemum cinerariaefolium) flower and Lomen grass (Cymbopogon citratus) leaf powders at three different doses (3, 4 and 5 g)/100 g of grain maize against maize weevil, Sitophilus zeamais Motsch. Their effectiveness was determined using different parameter such as grain damage and weight losses. The results revealed that all test materials at 5 g doses exhibited mortality action against maize weevil while at 3 g doses it gave the lowest percentage efficacy. Powdered leaves and seeds of neem and pyrethrum flower at 4 and 5 g were showed statistical significant (P<0.01) differences while powdered leaves of lemon grass at the similar rates were observed with moderately effectiveness and fresh leaves of hop bush gave the lowest mortality rate within 28 days of exposure in all tested doses. The result showed that the lower number of grains damaged in maize grains treated with botanical powders and the grain weight loss was also found low as compared to the untreated control. These findings suggest that botanical powders exert better mortality effect and hence reduced maize grain damage. It was also revealed that despite the high seed damage recorded in all botanical products, the S. zeamays numbers were relatively higher in untreated control while no grain seed damage was observed in standard check which was treated with Actellic dust. Maize grains treated with botanicals, indicated that insect reproduction and development were impaired in all botanical pesticides. However, all the doses tested for their insecticidal efficacy had an effect on the percentage weevil mortality and was found to be directly proportional to the amount of powder used. Therefore, The present study was suggested that Pyrethrum flower, neem leaf and seed powder can be used as good alternatives to chemical insecticides against S. zeamays due to their higher high mortality, lower grain damage and lower maize weight losses recorded as compared to untreated and synthetic insecticides. Key words: Botanicals, powder, mortality, maize weevil, Sitophilus zeamais, grain damage, actellic dust.