EFFECT OF CHLORPYRIFOS-METHYL ON OAT ECOSYSTEMS IN FARM GRANARIES

Chlorpyrifos-methyl was toxic to certain mite species when applied at 3.8 to 7.7 ppm on hulled oats Avena sativa or 3.1 to 5.0 ppm on hulless oats. Insecticide residues decreased by 65% in hulled oats and 50% in hulless oats in 1 yr and by 80% in hulled oats and 60% in hulless oats in 2 yr. Bioassay of treated oats with Tribolium castaneum adults for 24 h indicated 100% mortality above 4.7 ppm and negligible mortality below 2 ppm of insecticide. Chlorpyrifos-methyl virtually eliminated the predatory mites Androlaelaps casalis and Blattisocius keegani in treated compared with untreated hulled and hulless oats. Populations of another predatory mite, Cheyletus eruditus, were depressed but began to recover when the insecticide decreased below 0.6 ppm on hulled oats. In both types of oats, populations of prey mites Tarsonemus granarius and Acarus siro were unaffected by the insecticide. Other prey mite populations included Aeroglyphus robustus, which were moderately reduced, and Lepidoglyphus destructor and Paratriophtydeus coineaui, which were sharply reduced. Insecticide treatment had no effect on seed germination or microfloral infection. -from Authors