Interrelation of Moisture Content, Storage Temperature, and Dosage on the Effectiveness of Diazinon as a Grain Protectant Against Sitophilus oryzae (L.)1

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Abstract
Ramona wheat with a graded moisture range of 10, 13, and 16% was sprayed with acetone solutions containing the amount of diazinon necessary for deposits of 1.25, 2.5, 5, 10, and 20 ppm when applied at the rate of 10 ml/kg of wheat. Treated samples were stored in airtight, doubled, polyethylene bags inside cabinets thermostatically controlled to maintain 4 conditions of storage temperature, 2 with constant temperatures of 60° and 90°F, 1 with temperatures progressively increasing from 60°F, and another with temperatures progressively decreasing from 90°F at increments of 10°F for each 3-month interval during the year. The 2 criteria used for assessment of the effectiveness of diazinon deposits on wheat were the mortality and reproduction of the rice weevil, Sitophilus oryzae (L.), exposed to treated grain at various intervals after application of spray. The influence of moisture and temperature on the effectiveness of diazinon deposits was shown by reduced mortalities of the rice weevil, and increased number of progeny with increases in the moisture content or storage temperature of wheat. Dosages of 2.5 ppm and higher killed 100% of adult rice weevils in initial tests made 1 day after spraying, but effective dosage levels ranged from 5 ppm to 20 ppm for protection of test wheat over a long period of time. Less diazinon was required for protection of dry grain than grain stored at higher safe levels of moisture, and wheat stored at low temperatures required less diazinon for protection against the rice weevil than wheat stored at higher temperatures. These results indicate the desirability of adjusting dosages of diazinon to compensate for adverse effects of moisture and temperature that may be found in actual storage of grain.