Pesticide residues in stored wheat and their action on Sitophilus oryzae and Rhyzopertha dominica

The concern over supplying safe foods and discarding food lots with agrochemical residues over the legal limits has been the target of alerts from various agencies. Products derived from wheat are widely consumed in Brazil, and thus studies that aim at detecting agrochemical residues in this cereal grain and their risks are of utmost importance. The aims of this study were to evaluate the presence of agrochemical residues in wheat stored in a silo in Rio Grande do Sul and verify if there was residual action of the insecticides detected in the wheat. The first experiment consisted of multiresidue analyses of agrochemicals over a period of 10 months of storage. The second consisted of infesting samples from the previous experiment with Sitophilus oryzae and Rhyzopertha dominica to evaluate mortality. Nine agrochemicals were detected in the wheat, of which six were below the maximum limit of residues and three were above, according to Brazilian legislation. There was 100% mortality of Sitophilus oryzae after 96 h of exposure of this insect to the grain in all the samples evaluated, indicating that the residues of insecticide were still active even after the withholding period. No mortality was observed for Rhyzopertha dominica in the samples analyzed.