EFFICACY OF MALATHION AGAINST COLEOPTERAN POPULATIONS IN NEWLY-HARVESTED VERSUS YEAR-OLD STORED CORN

The impact of malathion treatment and duration of storage prior to tre atment on species composition and relative abundance of beetle pests w as investigated in shelled corn in newly-constructed galvanized steel bins. Corn was sampled monthly for insects with plastic probe traps fr om January through September 1989. Red and confused flour beetles, Tri bolium spp., hairy fungus beetle, Typhaea stercorea (L.), flat and rus ty grain and flour mill beetles, Cryptolestes spp., and foreign grain beetle, Ahasverus advena (Waltl), were most abundant in traps, but pla ster beetle, Cartodere constricta (Gyllenhal), minute brown fungus bee tle, Corti-caria pubescens (Gyllenhal), antlike flower beetle, Anthicu s spp., and larger black flour beetle, Cynaeus angustus (LeConte), als o were trapped. Greater numbers of the four major beetle species were trapped in older corn and in corn that was not treated with malathion and, depending on species, trap catch peaked in August or September. i nformation gathered during this investigation adds to our knowledge of insect infestation and insecticide application to on-farm stored corn and confirmed earlier reports that T. stercorea and A. advena potenti ally are pests of stored shelled corn. Thorough inspection and samplin g should be conducted throughout the storage period, but especially af ter grain temperatures warm above 20 degrees C.