Impact of Age on the Biological Activities of Sitophilus zeamais (Coleoptera: Curculionidae) Adults on Stored Maize: Implications for Food Security and Pest Management

The present work was undertaken in three successive years in three different regions of Nigeria to study the impact of age on the postharvest biological performance of maize weevil Sitophilus zeamais Motschulsky (Coleoptera: Curculionidae) adults infesting maize grain. Eight different age groups of S. zeamais adults which ranged from 1 to 56 d were used. The study assessed important parameters and was carried out using standard methods at mean temperature and relative humidity of 28.2°C and 87.5%, respectively. Results indicated that age affected bionomics of S. zeamais adult infesting maize grain in storage. The minimum age threshold for prolific oviposition in the females was 8 d. Weevils in the age groups 8-14 and 15-21 d showed highest fecundity. There was no effect of age on progeny emergence and development time for weevils younger than 36 d. Consequent upon infestation, only S. zeamais adults of ≤35 d old caused great damage and loss to grains in storage. The susceptibility of infesting weevil to cypermethrin was not greatly influenced by weevil age except at an elderly age of ≥43 d. Observations signal that weevil adults are physiologically fittest at ≤14 d old but indicate that adults of ≤35 d old pose the highest food security threat. The S. zeamais ecotype studied showed resistance to the pyrethroid insecticide at 24 h evaluation period and that also has implications for food security.