Chlorpyrifos-Methyl Degradation and Biological Efficacy Toward Maize Weevils (Coleoptera: Curculionidae) on Corn Stored at Four Temperatures and Three Moisture Contents

Abstract

Corn was treated with 6 ppm chlorpyrifos-methyl and stored for 10 mo at each of four temperatures (15.0, 22.5, 30.0, and 37.5°C) and three moisture contents (11.4, 12.4, and 14.4%). Every 2 mo, samples were removed from storage and analyzed for chlorpyrifos-methyl residue and infested with maize weevils, Sitophilus zeamais Motschulsky. Initial residues on the corn were 4.95 ± 0.67 ppm. Of the residues that were lost, most were lost during the first 2 mo of storage. The loss rate increased as temperature and moisture content increased. No weevils survived on corn stored at 15.0 or 22.5°C, except for 7.2% of the weevils that survived at month 10 on corn stored at 22.5°C. Weevil survival increased as moisture content increased in corn stored at 30.0 and 37.5°C. The threshold for weevil survival was ≈1.22 ppm chlorpyrifos-methyl. Population growth, the percentage of insectdamaged kernels, and dockage weight were all correlated with insect survival.