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℃ 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:

1. The median lethal doses (LD-₅₀) of the five insecticides against female adult cockroaches were: 0.40 µg/roach or 4.02 µg/body weight (gm) by Dieldrin, 0.29 µg/roach or 2.88 µg/body weight (gm) by D.D.V.P., 0.29 µg/roach or 2.96 µg/body weight (gm) by Diazinon, 0.54 µg/roach or 5.37 µg/body weight (gm) by Dibrom, and 2.96 µg/roach or 29.60 µg/body weight (gm) by Malathion. And those against male adult cockroaches were: 0.18 µg/roach or 3.29 µg/body weight (gm) by Dieldrin, 0.27 µg/roach or 4.89 µg/body weight (gm) by D.D.V.P., 0.16 µg/roach or 2.91 µg/body weight (gm) by Diazinon, 0.49 µg/roach or 8.97 µg/body weight (gm) by Dibrom, and 1.32 µg/roach or 24.19 µg/body weight (gm) by Malathion.

2. 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.

3. 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.

4. Amarked 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.