Mortality of Stored-Grain Insects Exposed to Microwave Energy

Abstract

Infestation of grain by insects is usually controlled with insecticides. Use of insecticides could result in residues in the food, which may have adverse effects on humans, and insects eventually develop resistance to insecticides. Hence, there is a need for an alternative method for disinfestation of grain. Disinfestation of harvested grains using microwaves can be one such alternative. A pilot-scale industrial microwave grain drying system operating at 2.45 GHz was used in this study to determine the mortality of three common adult stored-grain insects, namely, Tribolium castaneum, Cryptolestes ferrugineus, and Sitophilus granarius in barley and rye. Grain samples of 50 g each at 14%, 16%, and 18% moisture content (wet basis) were infested with adult insects. The samples were then exposed to microwave energy at four different power levels (200, 300, 400, and 500 W) for two exposure times (28 and 56 s). Complete (100%) mortality was achieved for all three species at 500 W for an exposure time of 28 s in barley and rye. For an exposure time of 56 s, complete mortality was achieved at 400 W for all the insects in barley and for C. ferrugineus in rye, but T. castaneum and S. granarius were killed at 300 W in rye. There was no significant difference in the mortality of insects in 14%, 16%, and 18% MC grain. Germination tests were conducted for barley and rye treated at different power levels and exposure times, and germination of seeds decreased with an increase in power level or exposure time or both.