Ability of Allophylus africanus (Sapindaceae) extracts and Azadirachta indica (Meliaceae) seed oil to protect maize against Sitophilus zeamais Motschulsky, 1855 (Coleoptera: Curculionidae) simulating farmer storage condition

Abstract

The weevil, Sitophilus zeamais Motschulsky (Coleoptera: Curculionidae) is the most important pest of stored maize worldwide. Experiments were carried out to evaluate the efficacy of Allophylus africanus P. Beauv (Sapindaceae) leaf extracts and Azadirachta indica A. Juss (Meliaceae) seed oil against S. zeamais under farmer storage conditions at the concentrations of 2.5, 5, 7.5, and 10 g/kg of maize. Each concentration is divided into two sets and wrapped in cotton then placed at two different places in 1 kg bag of maize. Maize bags were placed in 5 L containers and 40 adult insects were released inside and covered with a muslin cloth. Adult mortality, progeny inhibition and damage reduction were assessed. The obtained results showed that these tested extracts caused significant mortality to S. zeamais adults. Mortality % recorded 3.33%, 00.00%, 00.00% and 5.88% with neem oil, the methanol, acetone, and hexane extract of A. africanus at the concentration of 10 g/kg after one day post-infestation. Within 12 days of exposure, at the lowest concentration (2.5 g/kg), neem oil, methanol, acetone, and hexane extract caused 76.92%, 100%, 100% and 100% mortality, respectively. At the concentration of 10 g/kg, all the tested extracts completely inhibited F₁ progeny production, respectively. Moreover, these extracts reduced the grain damage and weight losses caused by weevils on maize. Considering the wide availability of A. africanus and neem trees, the application of extracts from both plants could be recommended as phytopesticides against maize weevils under storage conditions.