Search

A fumigation with dosage of 20 g/m3 sulfuryl fluoride was carried out in a warehouse stored 8 000 t of wheat and equipped with recirculation system, in which the temperature was 27～30 ℃ for head space,26～28 ℃ for top layer of the bulk, 16～19 ℃ for middle and bottom layers of central bulk and 26～29 ℃for surrounded bulk grain in the warehouse. The fumigant was applied in five points on the bulk surface and through the ventilation ducts under bottom of the bulk by a pipe connection while the recirculation running.The concentrations of sulfuryl fluoride in bulk surface, 1.5 m and 4.5 m depth under grain surface were all monitored during the process. The killing effect on Cryptolestes ferrugineus (Stephens) was also examined for the adults, pupae, larvae, and eggs of lab cultured strain and adults of field strain. The peak concentration was monitored on surface of the bulk and in the depth of 4.5 m of that, the concentration was lower in the depth of 1.5 m of the bulk, just after fumigant applied and while recirculation running. During exposure of 3 to 12 h, the sulfuryl fluoride concentration was above 20 g/m3 and distributed uniformly.The concentration of sulfuryl fluoride in the grain pile was generally higher, and the concentration decreased obviously with the time after 12 h. Sulfuryl fluoride concentration descended more quickly after 24 h when recirculation stopped and descended rate of sulfuryl fluoride concentration in higher temperature part of grain located in surround bulk was bigger than that in lower temperature part located in central bulk. When the concentration of sulfuryl fluoride in the grain pile decreased to 2 g/m3 (about 13 d), the decay rate decreased, and the time from 2 g/m3 to 0 g/m3 was about 10 days. During the fumigation that sulfuryl fluoride concentration changed in range of 27～24 g/m3, adults and larvae can be killed completely in 3 h exposure. Pupae can be given 100% mortality in 6 h when exposure under 27～22 g/m3 of the fumigation. The full mortality for eggs needed 24 h in 27～19 g/m3 of sulfuryl fluoride concentration. The tolerance of four life stages of C. ferrugineus to sulfuryl fluoride was eggs＞pupae＞adults≈larvae. In the grain bulk where temperature was 26～29 ℃ for top layer and surround bulk and 16～19 ℃ for middle and bottom grain of central bulk, all life stages of C.ferrugineus can be fumigated successfully by sulfuryl fluoride that concentration varied from about 24 g/m3 to 0 g/m3 during 23 d of the exposure time.