Rice Weevils and Maize Weevils (Coleoptera: Curculionidae) Respond Differently to Disturbance of Stored Grain

Rice weevils, Sitophilus oryzae (L.), and maize weevils, Sitophilus zeamais Motschulsky (Coleoptera: Curculionidae), are important pests of stored grain. We have observed that rice weevil adults have a greater propensity than maize weevils to climb upward after physical disturbance of stored grain. Our objective was to quantify this climbing behavior in both species under a variety of environmental conditions to assess whether our anecdotal observations were correct. We confirmed that, after a disturbance, significantly more rice weevils climb than maize weevils when reared on fresh wheat, Triticum aestivum L., and corn, Zea mays L., and at relatively low and high population density. This greater climbing tendency is apparently exclusively due to S. oryzae males, which climb significantly more often than females. This work not only elucidates the divergent evolutionary histories of these sibling species but also may provide useful information for the monitoring and control of these stored grain pests.