During the period from May to October 1969, the authors carried out a series of tests with the aim to ascertain the present status of susceptibility of adult cockraoches to various insecticides. The tests on the susceptibility of cockroaches to dieldrin, D.D.V.P., Diazinon; Dibrom, Malathion and lindane were performed with the topical application and the residual film methods under the conditions of 26 degrees C and 80% of relative humidity. The insects tested were collected from Seoul City and were reared at the laboratory. Some of the important results so far obtained can be summarized as follows: The median lethal doses (LD(50)) of the five insecticides against female adult cockroaches were: 0.4 ug/roach or 4.02 ug/body weight (gm) by Dieldrin, 0.29/roach or 2.88 ug/body weight (gm) by D.D.V.P., 0.29 ug/roach or 2.96 ug/body weight (gm) by Diazinon, 0.54 ug/roach or 5.37 ug/body weight (gm) by Dibrom, and 2.96 ug/roach or 29.60 ug/body weight (gm) by Malathion. And those against male adult cockroaches were: 0.18 ug/roach or 3.29 ug/body weight (gm) by Dieldrin, 0.27 ug/roach or 4.89 ug/body weight (gm) by D.D.V.P., 0.16 ug/roach or 2.91 ug/body weight (gm) by Diazinon, 0.49 ug/roach or 8.97 ug/body weight (gm) by Dibrom, and 1.32 ug/roach or 24.19 ug/body weight (gm) by Malathion. The level of susceptibility of adult cockroaches to the insecticides tested was 1.0-1.6 times higher as compared with the results obtained on the Japanese Takashi strain. The median knockdown times (LT(50)) of the female adult cockroaches by insectcides at 1% concentration of 3 mg per square centimetre were 1.82 hours by Malathion, 1.36 hours by Diazinon, 0.56 hours by Lindane, 0.50 hours by Dibrom, and 2.56 hours by D.D.V.P. A marked difference was seen to exist between the males and the females. The female cockroaches were more resistant than the male to Dieldrin, Diazinon and Malathion.
