Effects of insect population density and storage time on grain damage and weight loss in maize due to the maize weevil Sitophilus zeamais and the larger grain borer Prostephanus truncatus

A study was conducted with the objectives of assessing comparative grain damage and weight loss in maize due Prostephanus truncatus and Sitophilus zeamais at ten varying population densities (5, 10, 15, 20, 25, 30, 35, 40, 45 and 50 insects per 200 g grain) and three storage durations (30, 60 and 90 days), in a laboratory. The final insect densities, percent grain damage, flour (dust) produced and weight loss due to P. truncatus exceeded that of the S. zeamais. Mean final insect population density, percent dust production, and weight loss increased over the storage period for P. truncatus. However, percent dust production and weight loss did not show significant increase over the storage time for S. zeamais. Percent grain damage declined 60 days after grain storage for P. truncatus. However, percent grain damage increased sharply over the storage period for S. zeamais. A mean weight loss of 67.1 and 6.9% recorded at an initial population density of 50 insects 200 g -1 grain, after 90 days for P. truncatus and S. zeamais, respectively. Flour production by P. truncatus (52.8%) was higher than that of S. zeamais (1.2%) after 90 days due to extensive tunneling to the grain by the former. In conclusion, P. truncatus, caused high grain damage and weight loss, indicating that control measures should be designed at the onset of grain storage if the grain is planned to be stored for more than 30 days. Traditional grain storage facilities may not offer protection against P. truncatus, but promotion of the use of metal silos and resistant varieties in Kenya for grain storage is an alternative approach to reduce losses by P. truncatus.