Abstract
The rice weevil (Sitophilus oryzae) causes substantial post-harvest grain losses globally. With growing concerns over resistance and the safety of conventional fumigants, ethyl formate (EF) has emerged as a promising alternative due to its rapid action and minimal residue formation. This study systematically evaluated the efficacy of the EF fumigant against S. oryzae using 1-L laboratory bioassay chambers and a 9-L miniature silo system under varying environmental and operational conditions. In 1-L chambers, EF demonstrates concentration-dependent toxicity with lethal concentration (LC50) values of 18.8, 15.97, and 13.27 & micro;L/L at 30, 25, and 20 degrees C, respectively, following 4 h exposure. At 20-40 & micro;L/L and 30 degrees C, EF reduced larval and pupal emergence by 5- and 14.8fold, respectively, compared with the control, while achieving 75-100% adult mortality. By extending exposure from 4 to 24 h, the efficacy was substantially enhanced, increasing adult mortality from 8% to 70% at 15 & micro;L/L. However, grain loading significantly reduced performance, with mortality declining from 97% (0% loading) to 52% (90% loading), indicating EF's penetration limitations. Whereas, in the 9-L miniature silo, static fumigation (160 & micro;L/L, 24 h, 30 degrees C) produced highly position-dependent mortality: 100% (top), 35.5% (middle), and 20.3% (bottom). Importantly, forced air circulation resulted in 100% mortality across all positions, demonstrating that active airflow is essential for uniform fumigant distribution in grain-filled systems. The addition of CO2 enhanced the efficacy of EF, reducing the required EF concentration for complete mortality by 41.11% (from 80 to 65 & micro;L/ L), and LC50 dropped from 65.92 & micro;L/L in the control to 49.59 & micro;L/L at 30% CO2, representing a consistent of 1.32fold reduction in LC50 level. These findings establish EF as an effective fumigant against S. oryzae and highlight that exposure duration, grain loading, CO2 supplementation, and air circulation critically determine its practical efficacy for sustainable stored-grain protection.