Susceptibility of sorghum varieties to the maize weevil Sitophilus zeamais Motschulsky (Coleoptera: Curculionidae)

Abstract

Sitophilus zeamais Motsch. is one of the most important pests of sorghum in storage causing severe economic damage to the grain. Twenty-one sorghum varieties obtained from Haramaya University Sorghum Improvement Research Program were investigated for their relative resistance to S. zeamais attack. The Dobie index of susceptibility was used to group the varieties into different reaction categories. Among the twenty one sorghum varieties evaluated, only one variety, ‘WB-77’, was regarded as resistant to the weevil. All the remaining varieties were categorized as moderately resistant. Weevils reared on the resistant variety produced a few number of F1 progeny (20.00), had a high median developmental time (42.00 days) and a low percentage of seed damage (2.67) and seed weight loss (0.30). Percentage seed damage and weight loss are significantly and positively correlated with the mean number of F1 progeny emergence and are inversely associated with median developmental time. Consequently, those varieties with high number of F1 progeny scored high percentage of seed damage and weight loss. These results indicated that high lysine content was found to be the predominant factor in sorghum resistance to S. zeamais.