抄録
Female mosquitoes including Culex pipiens pallens, the main vector of Dirofilaria immitis, and some secondary vectors, were collected at 4 to 10 sites in Nagasaki City from 1983 to 1989 using light traps, and the number of the mosquitoes and the natural infection rate with D. immitis were compared between the southern and the northern parts of the city. In 1983, Cx. p. pallens was extremely prevalent in the southern part but not in the northern part. After 1986, the prevalence of Cx. p. pallens became very low in both the parts. The rapid decrease of prevalence of this species may be attributable to the decrease in breeding sites by improvement of roads and open roadside ditches in parallel with spread of sewage systems. On the basis of the number of infected mosquitoes in Nagasaki City, it was suggested that, Cx. tritaeniorhynchus and Ae. albopictus are important vectors in addition to Cx. p. pallens, but Ae. togoi does not play a significant role in the transmission of D. immitis.
