Corn weevil (Sitophilus zeamais Motsch.) and the effects of some organophosphorus insecticides as post-harvest grain and seed protectant in field corn
1992
Kriengkrai Jumroenma
Corn weevil, Sitophilus zeamais Motsch. is a major pest of corn and some cereal crops in storage. The infestation begins in the field. The weevils can damage stored grain or seed by feeding, lowering germination, producing off-odours, causing heat and creating conditions favorable to the growth of molds. The infestation is initiated in the field 90 days after planting, and is favored by an average moisture of 43.39 percent. The longer the harvesting time, in the case of Suwan 2602, and the more open husk cover, the greater the infestation. The rate of oviposition and survival were highest on corn of 16 percent moisture content at 25 deg C and 80 percent RH. Pirimiphos methyl, methacrifos and chlorpyrifos methyl are organophosphorus insecticides, which cause no hazard to consumers because their residues are almost destroyed in cooking. Methacrifos, pirimiphos methyl and chlorpyrifos methyl, at the rate of 5 mg/kg, were 100 percent effective in destroying S. zeamais for 6, 10 and 12 months respectively. Burned leaves, stunted or twisted stem and folded leaves occurred in seedlings treated with these insecticides, especially the highest rate of abnormal seedlings, 7.4 percent, was observed in the treatment of 320 mg/kg chlorpyrifos methyl. They had some effects on internal structure of corn seedlings and germination but the vigor of treated seeds were better than untreated seeds.
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