Pirimiphos Methyl as a Short Term Protectant of Grain Against Stored-Product Insects2

Abstract

Pirimiphos methyl ( O -[2-(diethylamino)-6-methyl-4-pyrimidinyl] O, O -dimethyl phosphorothioate), applied as a water emulsion (5, 10, and 20 ppm) to hard winter wheat and shelled yellow corn killed all exposed adult rice weevils, Sitophilus oryzae (L.), red flour beetles, Tribolium castaneum (Herbst), confused flour beetles, T. confusum Jacquelin duVal, and lesser grain borers, Rhyzopertha dominica (F.) at 24 h and 1 month after treatment; no F1 progeny developed. After 3 months, a few red and confused flour beetles survived exposure to grain treated with 5 ppm, but no progeny developed. Also, some lesser grain borers survived, and F1 progeny and damage were recorded in wheat treated with 5 ppm and in corn treated with 5 and 10 ppm. Malathion, applied at a calculated dosage of 10 ppm as the chemical standard, gave complete protection to both grains for 3 months. The residues of pirimiphos methyl degraded gradually as the storage period lengthened except for the 20 ppm applied to shelled corn. The residues of malathion de-graded gradually on both grains.