Estimation of the phosphine resistance level of the cigarette beetle, Lasioderma serricorne (Fabricius) (Coleoptera: Anobiidae), by the knockdown time of adult

In a previous study, the assay method was developed for determining easily and precisely whether cigarette beetles are knocked down by phosphine fumigation. In the study, it was shown that knockdown times and mortalities of adults exposed to phosphine fumigation were closely correlated to each other. However, it is important, for successful fumigation, to evaluate the susceptible level of eggs in the beetles' population beforehand because eggs are the least susceptible stage to phosphine of all the life stages of the beetle. Therefore, we investigated the correlation between the lethal concentration (LC) of eggs and the knockdown time (KT) of adults. The susceptible level to phosphine was investigated by a mortality test and a knockdown test for 15 strains. The correlation between the log LC of eggs and the log KT of adults was shown by the following logistic function showing a correlation coefficient of 0.933: log LC=0.370+(2.743-0.370)/[1+exp{-2.155×(log KT-2.521)}]. It was suggested that the substitution of the value of log KT_99.9 into the above logistic function yielded sufficient information for determination of the most appropriate phosphine concentration for successful fumigation.