The efficacy of ashes of four locally used plant materials against Sitophilus zeamais (Coleoptera: Curculionidae) in Cameroon

Abstract

Sitophilus zeamais Motschulsky is an important field-to-store pest of maize in several parts of Africa including Cameroon. Although synthetic insecticides are effective at controlling the pest, the environmental and health hazards of these chemicals are of increasing concern. This study assesses the efficacy of ashes of local plant material against S. zeamais in the western highlands of Cameroon as an alternative to synthetic insecticides. Laboratory studies on toxicity against F₁ progeny of S. zeamais were conducted using leaf ashes of Cupressus arizonica, Eucalyptus grandis, Ocimum gratissimum and root ash of Vetiveria zizanioides at the rates of 0.1, 0.25, 0.5 and 1.0 g/25 g maize grains in Kilner jars. Toxicity of E. grandis ash extract was also evaluated. The ashes of E. grandis and O. gratissimum at the rate of 0.25 g/25 g grains significantly reduced the number of emerged weevils. Eucalyptus grandis ash showed toxicity (1.0 F1 progeny emerging at 0.25 g/25 g grains compared with 16.5 for the control). Eucalyptus grandis ash at 20 g/2 kg grains significantly reduced grain weight loss and protected grains for 6 months without adversely affecting the germination of the seeds. Ethanolic E. grandis ash extracts at rates of 50,000 and 100,000ppm significantly (P, < 0.05) reduced the number of emerged F₁ progeny of S. zeamais.