Use of Solar Heat to Control Stored-Product Insect Pests : Bean Depth

Temperature in layers of different thicknesses of Azuki beans was measured and it was found that layer thickness was a very important factor to consider when an attempt is made to disinfest grains using solar heat. Thin layers of up to 3.0 cm required 1.5 hours to reach the temperature of 55℃, that is fatal, if exposure is done for 4 to 5 hours, deduced from the literatures, while still a thinner layer of 1.5 cm required only 30 minutes and a 4.5 cm thick layer never reached that temperature. The 1.5, 3.0 and 4.5 cm thick layers reached highest temperature of 78, 67 and 51℃ respectively. The 1.5 and 3.0 cm thick layers maintained temperature above 55℃ for 4 hours 50 minutes and 4 hours 20 minutes respectively. The 3.0 cm thick layer, therefore, seems the best and most practical. In general it is considered that very thick layers need a long time for the temperature to rise and do not reach so high, but keep the highest temperature attained for a fairly long time. On the contrary very thin layers have the temperature rise quickly but lose the heat rather rapidly. Therefore very thick or very thin layers being not convenient for solar heat disinfestation of insect pests, a suitable depth of grains need to be selected.