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

TL;DR

Microwave treatment can kill pests in stored paddy and improve their detection, while preserving grain quality.

Contribution

This study demonstrates microwave's dual role in pest control and detection in stored paddy.

Findings

Microwave treatment increased pest mortality and reduced fungal load in paddy.

Short microwave exposure improved recovery rates of specific insect pests.

Microwave treatment preserved key physical properties of paddy grains.

Abstract

Paddy (Oryza sativa L.) is one of the most important and high-yielding grains in the world. However, during storage, pests are often hidden within the protective layer formed by the husk, making them difficult to detect through conventional methods. Sitophilus oryzae, Tribolium castaneum, and Oryzaephilus surinamensis are three major pests that infest stored paddy. The current detection methods for these pests largely rely on traditional methods, which are time-consuming, labor-intensive, and are heavily based on manual operation. This study evaluated the potential of microwave treatment for controlling these pests and improving their adult’s detection in paddy samples. The results showed that as microwave power and exposure time increased, the survival rates of all three insect species and the fungal load in paddy decreased. Furthermore, moderate microwave treatment improved key physical properties of paddy, such as moisture content, water activity, and grain breakage percentage, thereby enhancing its storage stability. These findings suggest the possibility of developing an effective method for controlling insects and fungi to extend the storage quality of paddy. Additionally, short-duration and low-power microwave treatment significantly increased the recovery percentages of S. oryzae and T. castaneum, indicating the potential of this technique as a simple, rapid, and efficient method for detecting stored product insects in grain samples.

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 Sitophilus oryzae, Tribolium castaneum, and Oryzaephilus surinamensis increased with the increase in microwave power and exposure time. Specifically, 100% mortality was achieved for both S. oryzae and T. castaneum 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 S. oryzae adults, while microwave treatment at low power (350 W) with exposure durations of 25–40 s helps improve that of T. castaneum. 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.

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