碾米與銷售環境對小包裝米害蟲發生之影響

Effects of the milling process and grocery environments on the occurrence of stored-product insects

調查出廠小包裝米放置於室溫經三個月儲藏後，害蟲之發生情形發現糙米內發生米象（Sitophilus oryzae（L.））的蟲數遠高於白米。為探討米象發生原因，以小型碾米機碾製經10對米象產卵一週的稻穀成為糙米或白米，經儲藏一個月後，糙米中米象的發生數為116隻，與稻穀中米象數差異不顯著，經三個月儲藏，糙米中之米象數為780隻，則遠高於稻穀中米象數（155隻）。碾米後的白米，經儲存一個月無米象發生，經三個月儲藏後米象發生數為0.3隻，與糙米中米象數有明顯差異。以大型碾米機碾製儲存五個月的稻穀，結果亦相似，糙米之米象發生數遠高於白米。顯示稻穀碾製為糙米時，僅除去穎殼無法除去米象卵或幼蟲，因此米象密度未減少。糙米再碾製為白米時，因碾除大部分糊粉層僅剩胚乳部分，對米象卵或幼蟲有明顯破壞使蟲數劇減。以大型碾米機碾製後糙米、白米、水洗白米之害蟲相，除主要害蟲米象外，尚有稻穀中未發生的粉斑螟蛾（Cadra cautella（Walker））及外米綴蛾（Corcyra cephalonica（Stainton）），顯示小包米害蟲除包含從稻穀所帶來的蟲源外，碾米環境的污染所增加的害蟲也是小包裝米害蟲發生的另一來源。小包裝米碾米後儲藏於10℃環境，不論糙米或白米害蟲的發生均接近於零，與室溫環境儲藏有明顯差異，因此利用低溫環境儲藏將能有效降低小包裝米的害蟲發生。

"Rice pest samplings showed that small-bag brown rice was more prone to rice weevil (Sitophilus oryzae (L.)) infection than was small-bag milled rice after 3 months of storage following commercial milling. In a search for rice weevil sources in small-bag rice, rough rice subjected to a week of egg deposition by 10 pairs of rice weevils was milled into brown rice or milled rice using small milling machinery. After a month of storage, 116 rice weevils were found in the brown rice, and this number did not differ from that found in rough rice; however, 3 months later, 780 rice weevils had developed in the brown rice, a figure much higher than that found in the rough rice. On the other hand, no rice weevil was found in milled rice after a month of storage, and only 0.3 rice weevils on average occurred even after 3 months of storage. After 5 months of storage, rice processed by large milling machinery produced similar results of many more rice weevils occurring in brown rice compared to rough rice. These observations indicate that the mere removal of the husk from rice is insufficient to destroy rice weevil eggs and/or larvae, otherwise pest occurrence rates would have decreased. A further milling process to make brown rice into milled rice removes the major portion of the aleurone layer; meanwhile, this destroys pest eggs and/or larvae and largely reduces pest occurrence rates. Brown rice, milled rice, and washed milled rice processed by large milling machinery were also infected by Cadra cautella W. and Corcyra cephalonica S. which were not found in the rough rice. This led to the notion that stored-product insects might be introduced from other contamination sources through the milling processes in addition to the pest source from husks. After storage at 10 °C, both brown and milled small-bag rice had nearly no pests, a level which is significantly lower than that of rice pests found in rice stored at room temperature. Therefore, low-temperature storage can effectively reduce small-bag rice pest occurrence."