Disinfestation of stored grain insects using microwave energy
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Disinfestation using microwaves can be an alternate to chemical methods of killing insects in grain. A pilot-scale industrial microwave dryer operating at 2.45 GHz was used to determine the mortality of life stages of Tribolium castaneum (Herbst), Sitophilus granarius (L.) and Cryptolestes ferrugineus (Stephens) adults in wheat, barley, and rye. Grain samples of 50 g each at 14, 16, and 18% moisture content were infested with stored-grain insects. The samples were then exposed to microwave energy at 200, 300, 400, and 500 W for exposure times of 28 and 56 s. Complete (100%) mortality was achieved for adults of three insect species at 500 W, 28 s and at 400 W, 56 s in barley and wheat. In rye, complete mortality of adult T. castaneum and S. granarius was achieved at 400 W, 28 s and at 300 W, 56 s whereas for C. ferrugineus, complete mortality was achieved at 500 W, 28 s and at 400 W, 56 s. The average temperature of wheat, barley, and rye at 500 W and 28 s was around 80, 71 and 82oC, respectively, and moisture loss was 2.0, 1.9 and 2.5 percentage points, respectively. Among the life stages of T. castaneum in wheat, eggs were the most susceptible followed by larvae, and the least susceptible were the pupae and adults. Among the life stages of T. castaneum in barley and rye, eggs were the most susceptible and adults were the least susceptible with no significant difference between pupae and larvae. There was no significant difference in the mortality of adults at 14, 16, and 18% moisture content barley and rye and the life stages of T. castaneum and S. granarius in rye. Germination of seeds decreased with an increase in power level or exposure time or both. There was no significant difference in the quality characteristics of microwave-heated wheat and rye except for reduced flour yield in rye. The quality of the barley treated at 500 W, 28 s was the same as the control, whereas, there was significant decrease in the quality of barley treated at 400 W, 56 s.