Biological Effects of Neem Oil and Neemazal against the Larger Grain Borer, Prostephanus Truncatus (Horn) (Coleoptera: Bostrichidae) on Stored Maize

Abstract

The biological activity of neem oil and neemazal against the larger grain borer, Prostephanus truncatus (Horn) was assessed in maize grain in the laboratory. The bioassays carried out were toxicity of the products against adults and immature stages, effect of the products on progeny production, damage assessment, repellent action and persistency of the products in grain and their effect on seed viability. Neemazal was highly toxic to P. truncatus than neem oil. The highest dosage of 0.8 ml killed 100 % adults of P. truncatus after 72 h exposure but the same dosage of neem oil evoked 70 % mortality after 96 h. The products were also active against the eggs and larvae causing a significant mortality. Neemazal provided greatest protection of maize grains with no noticeable feeding holes on grains treated with 0.6 and 0.8 ml/gm. Both products were moderately repellent to P. truncatus causing less than 50 % repellency. Activity of the two products significantly declined in treated grain after 24 h of storage following treatment. Neem oil and neemazal increased water absorption by maize seeds. Furthermore, seed germination was not affected by neem oil but neemazal significantly reduced seed germination. For the control of P. truncatus in stored maize, neemazal offers greatest protection against both the immature stages and adults. The non-toxicity of neem products to man and other beneficial organisms emphasize the potential use of these products as protectants of farm gate grain storage of small holdings in rural communities in Ghana and other parts of Africa where the neem is abundant.