Epidemio-entomological Surveys in Vector Mosquitoes of Japanese Encephalitis in Kyongbuk, Korea*

Abstract

The seasonal prevalence and population dynamic of Culex tritaeniorhynchus (Cx. tritaeniorhynchus) in relation to the epidemic of Japanese encephalitis, and the epidemio-entomological surveys of this vector mosquito in Kyongbuk Province, Korea were made during the period of 15 years spanruing from 1984 to 1998. As in the general patterns of seasonal prevalence, Cx. tritaeniorhynchus was first collected between early and late June, and peaks in the population densities of Cx. tritaeniorhynchus, occurred during the period from late July in 1987 and 1994, early- to late-August in 1984-1986, 1990-1993 and 1995, and early- and mid-September in 1988, 1989 and 1996-1998. they showed a simple sharply pointed one-peak curve. There was a gradual decrease from mid- September, accompanied by with a very small number of them collected until late October or early November in every year, except 1990. Cx. tritaeniorhynchus with nocturnal biting habits had two peaks in their daily activities, one soon after the sunset and the other during a few hours' period from 2-3 o'clock, although the relative numbers collected varied and the highest peak collection occurred at different time in a night. The total number of larval Cx. tritaeniorhynchus in rice fields was the highest in mid-August, and its number progressively decreased in early September due to insecticides sprays. After late September, the larvae was rarely found until rice plants were harvested. The larval Cx. tritaeniorhynchus showed high resistance against five organophosphorus compounds. In the adult horizontal life table characteristics of Kyongsan colonies of Cx. tritaeniorhynchus under insectary conditions, life expectancy was 28.3 days for males and 59.8 days for females. The net reproductive rate was 7.8 days, and generation time was 25.6 days.