Effects of Grain Moisture Content on Residual Toxicity and Repellency of Malathion1

Abstract

Malathion applied at 2 p.p.m. to wheat of 13.5% moisture content caused 99% mortality of the rusty grain beetle, Laemophloeus ferrugineus (Steph.) at 8 months after treatment; the wheat was stored in airtight containers at 48° F. A dosage of 16 p.p.m. was required for comparable control in wheat of 15.5% moisture content but this dosage was ineffective in wheat of 18% moisture content at 5 months after treatment. Repellency tests in wheat of 12, 15 and 17% moisture content treated at 4 or 8 p.p.m. the test insects being placed in adjoining untreated wheat, showed that adults of L. ferrugineus but not of sitophitus granarius (L.) were repelled from wheat of 12% moisture content treated at 4 p.p.m.: mortalities of both species ranged from 84.8 to 100.0% in treated wheats. Reproduction of L. ferrugineus was reduced more than that of S. granarius in unevenly treated wheat. There was no adverse effete on the milling or baking quality of wheat treated with malathion at 4 or 8 p.p.m.