Susceptibility of the Cigarette Beetle Lasioderma serricorne (Fabricius) to Phosphine, Ethyl Formate and Their Combination, and the Sorption and Desorption of Fumigants on Cured Tobacco Leaves

The susceptibility of Lasioderma serricorne to phosphine (PH3), ethyl formate (EF) and their combination (PH3 + EF) was evaluated in this study. Eggs, larvae, pupae and adults were subjected to treatment with fumigants to determine the 90% lethal concentration time (LCt90) values. Treatment with PH3 for 20 h resulted in LCt90 values of 1.15, 1.39, 14.97 and 1.78 mg h/L while treatment with EF resulted in values of 157.96, 187.75, 126.06 and 83.10 mg h/L, respectively. By contrast, the combination of PH3 + EF resulted in LCt90 values of 36.05, 44.41, 187.17 and 35.12 mg h/L after 4 h. These results show that, through treatment with PH3 + EF, control can be achieved at lower concentrations than for treatment with EF alone and at lower exposure times than for treatment with PH3 alone. The sorption rates of the fumigants on cured tobacco leaves were determined for filling ratios of 2.5%, 5.0% and 10.0% (w/v). Cured tobacco leaves were treated with either 2 mg/L PH3, 114 mg/L EF or 0.5 mg/L PH3 + 109 mg/L EF. Treatment with PH3 showed sorption rates of 0.0%, 7.1% and 14.3%. EF, however, showed higher sorption rates of 64.9%, 68.5% and 75.5%, respectively, for the indicated filling ratios. When PH3 and EF were combined, the sorption rate of PH3 was 0.0%, while the sorption rates of EF were lower (9.1%, 12.0% and 23.2%) than treatment with only EF. EF required a ventilation time of longer than 22 h to desorb from cured tobacco leaves. Therefore, PH3 + EF can effectively control L. serricorne in cured tobacco leaves, with sufficient ventilation time required after treatment for the safety of workers.