Efficacy of some plant extracts as a safe and sustainable management option for Sitophilus zeamais (Motschulsky) in stored maize

Abstract

The use of synthetic chemical insecticides has proven effective in controlling insects. However, indiscriminate use is associated with a variety of health and environmental problems. Plantbased products could be an alternative for pest control because of their natural originality, low/non mammalian toxicity, biodegradability, zero residual effect and accessibility. A survey conducted in the Southern part of Volta region in Ghana collected data on plant species used as maize protectants. A total of eleven plant species were obtained. Seven out of the eleven were selected based on their availability and accessibility including lemon grass (Cymbopogon citratus), basil (Ocimum basilicum), Acheampong leaves (Chromolaena odorata), garlic (Allium sativum), Africa scent leaf (Ocimum gratissimum), guava leaves (Psidium guajava), onion (Allium cepa) for preliminary screening. Four most efficacious species (Cymbopogon citratus, Psidium guajava, Ocimum basilicum and Ocimum gratissimum) were selected for further work in the laboratory at 28±2°C, 65% RH and 12D:12L against S. zeamais. The assays were conducted by treating 50 g of maize with methanol extracts at the rates of 0.2, 0.3, 0.4 and 0.5 g/mL. Contact toxicity, repellency, effects on oviposition, development, seed damage, and weight loss were assessed. The extracts significantly (p ≥ 0.05) reduced emergence of progeny from adult weevil, eggs and immature stages. The extracts had a reproduction inhibition rate of 81–100%. The extracts protected maize against damage by S. zeamais for 12 weeks. Maximum weight loss and seed damage of 11.3% and 8.7%, were recorded compared to control with 21.4% and 24.7%, respectively. The extracts could therefore be used as alternatives for synthetic insecticides.