Laboratory Evaluation of Cotton (Gossypium hirsutum) and Ethiopian Mustard (Brassica cariata) Seed Oils as Grain Protectants against Maize Weevil, Sitophilus zeamais M. (Coleoptera:Curculionidae)

Abstract

Maize is the second most widely grown cereal crop in Ethiopia. In storage, maize is severely destroyed by storage insect pests, mainly maize weevil (Sitophilus zeamais). In an effort to develop a non-synthetic pesticide control approach, a study was conducted to determine the efficacy of two cooking oils, Ethiopian mustard (Brassica carinata) and cotton (Gossypium hirsutum), to control S. zeamais under laboratory conditions. The oils were applied at the rate of 0.2 to 0.5 ml per 250 g of grain and compared with untreated control and malathion super dust as standard check. The study was laid-out in completely randomized design (CRD) with three replications for each treatment. The efficacy of the oils was assessed on the basis of total insect mortality, median lethal time (LT50), weevil progeny emergence, seed hole’s number, weight loss and germination rate. The results showed that the oils caused 25 to 100% mortality at the different concentrations used. Both oils had LT50 of 0.5 day when applied at the concentration of 0.5 ml. At concentration of 0.3 to 0.5 ml, both oils caused zero weevil progeny emergence, minimum seed damage, zero grain weight loss and 89.2 to 95.5% seed germination rate which were similar to those of malathion (Diethyl succinate) and significantly different from those of the untreated control. The tests demonstrated that the two oils are effective stored maize grain protectants and can be used as components of maize weevil integrated pest management option. Key words: Cooking oils, maize weevil, Sitophilus zeamais, mortality, stored grain.