Effects of Microwave on Mortality and Detection Efficiency of Three Stored Grain Insect Adults in Stored Paddy, and on Grain Quality

Microwave heating has been widely used for disinfestation in the food industry due to its selective heating. However, research on the effects of microwave heating on stored product insects is still relatively limited, which has restricted its broader application in grain pest control storage. Therefore, this study evaluated the lethal effects of different microwave powers and exposure times on three major pests in paddy and investigated the impact of microwave treatment on improving adult detection efficiency, intending to develop a rapid and efficient detection method for stored grain insects. The results showed that the mortality of <i>Sitophilus oryzae</i>, <i>Tribolium castaneum</i>, and <i>Oryzaephilus surinamensis</i> increased with the increase in microwave power and exposure time. Specifically, 100% mortality was achieved for both <i>S. oryzae</i> and <i>T. castaneum</i> at 700 W for 60 s exposure. However, higher power levels and longer exposure durations exacerbated the non-uniformity of grain temperature distribution and adversely affected the germination rate. In addition, microwave treatment at 350 W, 490 W, and 700 W significantly reduced fungal load in paddy. The moisture content and water activity of rice decreased with the increase in microwave power and exposure time, while the percentage of grain breakage remained largely unaffected. These findings indicated that microwave treatment can effectively control insects and fungi without significantly altering the main physical properties of paddy. Notably, microwave treatment with short exposure durations (20-30 s) at all three power levels is conducive to increasing the recovery percentage of <i>S. oryzae</i> adults, while microwave treatment at low power (350 W) with exposure durations of 25-40 s helps improve that of <i>T. castaneum</i>. Accordingly, microwave heating is not only a promising strategy for protecting stored grains but also has potential for development as a rapid detection method for specific insect pests.