Effects of biopesticides extracted with a homemade solvent on stored maize protection

Abstract

Synthetic chemicals continue to play an important role in reducing storage losses attributable to insect pest activities. However, the adverse effects associated with some patented chemicals make synthetic pesticides less attractive and have given the drive to search for alternative methods of pest control. This study evaluated the effects of a traditional gin, akpeteshie crude extracts made of four timber species, neem (Azadirachta indica), mahogany (Khaya senegalensis), teak (Tectona grandis) and cedrela (Cedrela odorata) on the maize weevil Sitophilus zeamais on stored maize grains in the laboratory. Home-made extracts of the test tree plants at concentrations of 0.5, 1.0 and 2% were tested as grain protectants or as insect poisons. All tested extracts in their respective concentrations performed well in the reduction of live insects during maize storage as compared to a non-extract treatment. The mode of action of all the extracts was generally concentration and time-dependent. On average neem extract was the most effective followed by mahogany, teak, and cedrela in that order. Neem and mahogany extracts performed well in reducing grain damage at a concentration of 2% and at 0.5% concentration of cedrela extract respectively. All extracts reduced progeny emergence and acted both as a repellent or a toxicant. The extracts performed better as compared to the untreated control in the viability of maize seeds leading to germination, and subsequent seedling emergence. The relatively low weight loss of the stored grains treated with these crude extracts during the 90-day experimental period at a maximum concentration of 2% is predictive that they can be adopted as safe and alternative grain protectants against weevils in store. The unknown phytochemicals in these akpeteshie hardwood extracts may be responsible for the insecticidal properties against the weevils. For some concentrations of the extracts, germination was inconsistent which led to the suspicion of allelopathy.