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We undertook laboratory bioassays to evaluate the insecticidal effect of spinosad dust against two major stored-grain beetle species, Rhyzopertha dominica (F.) and Sitophilus oryzae (L.), in wheat, barley and maize. Spinosad was applied at four dose rates: 20, 100, 500 and 1000 ppm of the formulation, corresponding to 0.025, 0.125, 0.625 and 1.25 ppm of active ingredient, respectively. Adult mortality was measured after 7 and 14 days of exposure in the treated substrate, while progeny production was assessed after the removal of the parental adults. For R. dominica, adult mortality was high and reached 100% at doses 0.125 ppm of a.i. after 14 days of exposure. In contrast, mortality of S. oryzae adults was 495% after 14 days of exposure only at 1.25 ppm of a.i. With the same exposure interval, no significant differences were noted in R. dominica mortality levels among the three grains tested, while mortality of S. oryzae was significantly higher on wheat than on barley and maize. More adult progeny were recorded for S. oryzae than for R. dominica. A simple and reliable method using high-performance liquid chromatography/mass spectrometry method (LC/MS) was developed for the precise and selective quantitative determination of spinosyns residues in wheat, barley and maize grains. Spinosad dissipation on different commodities such as maize, barley and wheat differed significantly. Accelerated degradation of spinosad was observed in maize grains 14 days after application; the concentration of spinosad was slightly decreased in barley, but in the case of wheat a negligible degradation of spinosad was observed. These findings suggest that the reduced mortality of S. oryzae in maize is probably due to the high degree of pesticide degradation.

No abstract

The insecticidal effect of spinosad dust, a formulation that contains 0.125% spinosad, was evaluated against adults of Sitophilus oryzae (L.) and Rhyzopertha dominica (F.) at three temperature levels (20, 25, and 30 degrees C) and four commodities (wheat, Triticum aestivum L.; barley, Hordeum vulgare L.; rice, Oryza sativa L.; and maize, Zea mays L.). For this purpose, quantities of the above-mentioned grains were treated with spinosad at two dose rates (20 and 50 ppm of the formulation, corresponding to 0.025 and 0.06 ppm AI, respectively), and mortality of the exposed adults in the treated grains was measured after 7 and 14 d, whereas progeny production was assessed 65 d later. Generally, for both species, mortality increased with dose, exposure interval, and temperature. For S. oryzae, adult survival and progeny production were lower on wheat than the other grains. After 14 d of exposure, mortality of S. oryzae adults on wheat treated with 50 ppm ranged between 61 and 98%, whereas in the other three commodities it did not exceed 42%. Mortality of R. dominica after 14 d on grains treated 50 ppm ranged between 91 and 100%. For this species, progeny production from exposed parental adults was low in all commodities regardless of temperature. Results indicate that spinosad dust can be used as an alternative to traditional grain protectants, but its effectiveness is highly determined by the target species, commodity, dose, and temperature.

The insecticidal effect of spinosad dust, a formulation that contains 0.125% spinosad, was evaluated against adults of Sitophilus oryzae (L.) and Rhyzopertha dominica (F.) at three temperature levels (20, 25, and 30 degrees C) and four commodities (wheat, Triticum aestivum L.; barley, Hordeum vulgare L.; rice, Oryza sativa L.; and maize, Zea mays L.). For this purpose, quantities of the above-mentioned grains were treated with spinosad at two dose rates (20 and 50 ppm of the formulation, corresponding to 0.025 and 0.06 ppm AI, respectively), and mortality of the exposed adults in the treated grains was measured after 7 and 14 d, whereas progeny production was assessed 65 d later. Generally, for both species, mortality increased with dose, exposure interval, and temperature. For S. oryzae, adult survival and progeny production were lower on wheat than the other grains. After 14 d of exposure, mortality of S. oryzae adults on wheat treated with 50 ppm ranged between 61 and 98%, whereas in the other three commodities it did not exceed 42%. Mortality of R. dominica after 14 d on grains treated 50 ppm ranged between 91 and 100%. For this species, progeny production from exposed parental adults was low in all commodities regardless of temperature. Results indicate that spinosad dust can be used as an alternative to traditional grain protectants, but its effectiveness is highly determined by the target species, commodity, dose, and temperature.