Abstract
Since 1964 we have been engaging in checking the development of insecticide resistance in German cockroach, Blattella germanica. Samples of cockroaches were collected from about twenty different places of Japan. The results may be summarized as follows : Females of the field colonies showed less than 50% mortality to dieldrin at 0.25g/m^2 after 7 days' continuous exposure. Even at 2.5g/m^2, several colonies showed only low mortalities not attaining 50%. On topical application test these resistant cockroaches showed (LD)_<50> values against dieldrin after 7 days at least 370 times that of the normal strain. The dieldrin-resistant colonies were also resistant to γ-BHC and chlordane, the (LD)_<50> value being about 20 times the normal for γ-BHC and about 60 times for chlordane. These resistant colonies were found to be still quite susceptible to organophosphorus compounds such as fenitrothion and diazinon.
