Physical disturbance as a non-chemical approach to control weevils in stored maize

Maize is among the top three kinds of cereal grown in the world, and a daily source of food calories for over 50% of the populace in Sub Saharan Africa (SSA). Since the population of SSA will double by the year 2050, the demand for maize will triple following this trend. Maize weevils (Sitophilus zeamais) cause significant post-harvest losses of untreated stored maize. To meet the future demand of maize in SSA, post-harvest interventions are necessary to reduce tonnages of maize lost from stored grain insect pests. Research in using physical disturbance has been effective in reducing populations of weevils in stored maize. Unlike chemical treatment, the disturbance approach is cost-effective and does not leave residues in the food supply chain. In this context, this study investigated physical disturbance as a non-chemical approach to suppress maize weevils in stored maize. The study included: i) design and construction of automated physical disturbance machines, ii) determining the best physical disturbance time interval that suppresses weevils in stored maize, and iii) stirring of maize stored in an on-farm bin to suppress maize weevils. The first experiment tested the disturbance machines on infested maize rotated through about 1.25 revolutions in 3 seconds. The initial population of 25 live maize weevils reduced in a range of 1 to 4 weevils at all machine run times. The absence of physical damage on the appendages of adult maize weevils indicated that the selected disturbance rate of 1.3 m/s did not injure adult maize weevils. The second experiment determined the effective disturbance over time to reduce populations of maize weevils. The results showed that disturbance intervals of 8, 12, and 24 h reduced the populations of maize weevils by 75%, 95%, and 94%, respectively, compared to the undisturbed jars after 160 days of maize storage. In addition, the results indicated that disturbance once per day was the best interval in controlling weevil populations after 160 days of maize storage. The quality of maize in the disturbed jars was better than that in the undisturbed jars. The third experiment evaluated the effect of mechanical stirring infested maize on the population of weevils in a corrugated steel bin filled with 127 Mg of maize. While the population of live maize weevils in the unstirred bin was increasing, stirring achieved 100% control of S. zeamaiz after 40 days. Additionally, maize in the stirred bin was of better quality compared to maize in the unstirred bin. Overall, disturbance once per day (24 h) was effective in suppressing maize weevil populations during grain storage. This non-chemical approach is simple and affordable and holds great potential for the smallholder farmers to protect their stored maize. This study also documented that physical disturbance can be scaled-up using commercially available stirring machines to suppress stored grain insects in grain bins with a storage capacity up to 1651 Mg