Evaluation of Chlorpyrifos-Methyl and Chlorpyrifos-Methyl plus Methoprene as Protectants of Stored Corn: Small Bin Tests

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Abstract
Chlorpyrifos-methyl applied at 6 ppm and a combination of 6 ppm chlorpyrifos-methyl + 1 ppm methoprene were evaluated as protectants of stored corn (Zea mays L.) against a standard malathion application of 8 ppm and an untreated control. Corn was treated in October 1987, placed in 10-, 19-, and 76-bu bins, and infested at selected intervals with red flour beetle, Tribolium castaneum (Herbst); flat grain beetle, Cryptolestes pusillus (Schonherr); maize weevil. Sitophilus zeamais Motschulsky; and Indianmeal moth, Plodia interpunctella (Hiibner). Indianmeal moths did not establish populations on treated or untreated corn. Beetle populations in untreated controls were not abundant until June 1988 (8 mo after application). After 12 mo, red flour beetle and flat grain beetle populations were significantly greater in corn treated with malathion than in corn treated with either chlorpyrifos-methyl or chlorpyrifos-methyl + methoprene. Maize weevil populations were not significantly different among the three chemical treatments. Moisture content was not significantly different between treated and untreated corn or among the chemical treatments. Dockage and weight loss were significantly greater in untreated than in treated corn after 8 mo. After 12 mo, weight loss was significantly greater in malathion-treated corn than in corn treated with either chlorpyrifos-methyl or chlorpyrifos-methyl + methoprene. Insect population levels or insect damage did not differ significantly between the latter two treatments.