[Population density of chigger mites, the vector of tsutsugamushi disease in Chollanam-do, Korea].

The geographical distribution and population density of rodents and chigger mites at six localities of Chollanam-do were investigated from October to December in 1993. Among total 142 field rodents collected by the modified Chemla wooden traps, 131 rodents were Apodemus agrarius (92.3%) and 11 were Crocidura lasiura (7.7%). Out of 142 field rodents, 92 were parasitized by chiggers, showing 69.0% of the infestation rate and 74.2 of the chigger index. Infestation rate and chigger index of A. agrarius and C. lasiura were 73.3%, 80.4 and 18.2%, 0.5, respectively. From the trapped field rodents, 10,532 chiggers were collected and identified with 11 species of 4 genera. Leptotrombidium pallidum, the vector species of tsutsugamushi disease, was the dominant species, showing 8,038 chiggers (76.3%). L. scutellare was the second dominant species showing 1,359 chiggers (12.9%). The distribution of chigger mites was clearly localized by the species, showing the different dominant species according to localities. The predominant species was L. scutellare (100%) in Changhung-gun, L. scutellare (41.5%) in Posong-gun, L. pallidum (88.8%) in Hwasun-gun, L. pallidum (59.2%) in Koksong-gun, L. zetum (77.3%) in Hampyong-gun, and L. palpale (63.4%) in Tamyang-gun. Regarding to the geographical distribution of chigger population density, the infestation rate and chigger index was most high in Hwasun-gun as 62.4% and 216.2 respectively, and next high in Koksong-gun as 22.4% and 77.7% respectively.