| Summary: | Phosphine resistance is occurring among stored-grain pests worldwide. This study investigated the fumigation activity of phosphine (PH<sub>3</sub>) and carbonyl sulfide (COS) against domestic strain (d-strain) <i>Tribolium castaneum</i>, resistance strain (r-strain) <i>T</i>. <i>castaneum</i> and <i>Oryzaephilus surinamensis</i>. All developmental stages of the pests were exposed to two fumigants (PH<sub>3</sub> and COS), and the fumigation activity according to the dose and exposure time was evaluated in a 12-L desiccator and 0.5 m<sup>3</sup> fumigation chamber. The rice sorption rate and quality following exposure to thetwofumigants were evaluated. The mortality was 2.9% in r-strain <i>T</i>. <i>castaneum</i>, 49.5% in d-strain <i>T</i>. <i>castaneum</i> and 99.2% in <i>O</i>. <i>surinamensis</i> when 2 mg/L PH<sub>3</sub> was used in a 12-L desiccator for 4 h. However, all pest developmental stages showed 100% mortality after 24 h of exposure in the 0.5 m<sup>3</sup> fumigation chamber, except for the r-strain <i>T</i>. <i>castaneum</i>. A mortalityof 100% was observed in all of the r-strain <i>T</i>. <i>castaneum</i> developmental stages at an exposure time of 192 h. For COS applied at 40.23 mg/L and 50 g/m<sup>3</sup> in the 12-L desiccator and the 0.5 m<sup>3</sup> fumigation chamber, respectively, 100% mortality was observed across all developmental stages regardless of species and strain. The sorption of COS was 10% higher than that of PH<sub>3</sub>, but there was no significant difference in rice quality compared to that in the control. Therefore, this study suggests that COS can be used for controlling <i>T</i>. <i>castaneum</i> resistant to PH<sub>3</sub>.
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