Normal Bangkok strain of X. cheopis which had little resistance to DDT in 1966 became moderately resistant in 1972 without any direct exposure to the insecticide. It was analyzed that the causes of resistance gaining were as follows. First, the possibility of being exposed unconsciously to DDT spray under malaria eradication program could not be ruled out, even in laboratory as far as ventilation windows would be open sometime. Insecticides from air spray through the window influenced the fleas kept in the pools. Second, it may be said that initial resistance to DDT has become greater and greater ecologically without any exposure of insecticides. A highly resistant strain of X. cheopis which survived after contacting 4% DDT for five times during one year period was obtained in the laboratory and it showed 100% survival at the highest concentration (4%) of DDT paper by 24 hour exposure. The hybrid forms between normal Bangkok strain and artificially mutated "Resistant Strain" were obtained by mixing the above two colonies. Regardless to the sexes of both ancestors, the results of resistance tests of hybrids showed that artificially gained resistance of fleas to DDT was inherited possibly by recessive hereditary role by pheonotype.
parasitology-arthropoda-flea-Xenopsylla cheopis ; resistance-DDT ; Bangkok strain ; DDT

The results of the tests carried out in 1971 strongly suggested that a considerable portion of the flea population in MR 2 had developed resistance not only against DDT but also malathion and dieldrin. There is also the possibility of the fleas developing a resistance to diazinon and lindane. Thus careful consideration should be given to the continuous use of diazinon. In areas where fleas had developed a resistance to malathion, further tests should be conducted continuously to confirm the possible development of resistance. Other insecticides which have not been used in Vietnam for any purpose should be ready to be substituted, if the development of resistance is confirmed.
parasitology-arthropoda-flea-Xenopsylla cheopis ; resistance ; Vietnam ; DDT ; dieldrin ; diazinon ; lindane ; malathion

A survey on rats and rat-fleas was performed in costal area of Korea during 1972 in Inchon, Kunsan, Yosu, Busan and other areas. The number of the caught rats was 1,448. Total number of collected fleas was 2,480. Geographical distribution were described. Flea index was in 1.71 total. Mothly flea indices were 0.35-0.84 in January to March, 2.13-2.59 in April to June, 0.58 in July and 1.82-4.91 in August to November. Mortality rate of X. cheopsis to various concentration of DDT in 1 hour exposure were 43.8 % in 4.0 %, 30.4 % in 1.0 %. In 24 hours exposure, the mortalities were 100 % in 4.0 %, 91.5 % in 2.0 %, 73.5 % in 1.0 % and 37.0 % in 0.5 % DDT.
parasitology-arthropoda-flea ; rat ; Xenopsylla cheopis ; Monopsyllus anisus ; Nosopsyllus fasciatus ; Leptopsylla segnis ; Ctenophthalmus cong. congeneroides ; Ctenocephalides canis ; Nosopsyllus nicanus ; Rhadinopsylla attenuata ; epidemiology ; insecticide ; DDT-chemotherapy ; DDT