In order to determine population dynamics of Anopheles sinensis, a survey based on average number of female mosquitoes per trap-night was carried out during the period of 5 years from 1987 to 1991. A. sinensis first appeared between the 2nd and 20th April, and were trapped in large number between the 5th and 12th July. The number of trapped mosquitoes began to decrease from mid-August, and a few were collected until mid-November, each year. The average number of A. sinensis in July was 542.6 per trap-night in 1987, but in 1989 increased abruptly to 1,331.4, and then decreased to considerably lower levels, 271.9 in 1990 and 372.1 in 1991. The nocturnal activity of A. sinensis to attack humans was found to become active in the early night, and it was gradually decreasing at mid-night, however, then slightly increasing toward dawn. The immature stage of A. sinensis in the rice paddies was first found in the correlation pattern with peak adult densities in early July. The highest larval density of A. sinensis in the study area was 21,226 x 10(3) in early July 1990. The larval A. sinensis showed high resistance level and resistance ratios against 3 kinds of organo-phosphorous compounds, diazinon, malathion, and fenitrothion, but low resistance against fenthion. The present results indicated that the population density of A. sinensis in Kyongbuk area is decreasing over the five-year from 1987 to 1991.
