Population Dynamics on Vector Mosquitoes in Kyungpook; Korea

Abstract

In order to determine the seasonal prevalence and population dynamics of vector mosquitoes in Kyungpook Province, Korea, a survey based on the average number of female mosquitoes per trap-night, were carried out during the period from 1992 to 1995. A.sinensis first appeared between late March and early May, and were trapped in a large number between 29th June and 8th July. The number of trapped mosquitoes began to decrease from early September, and a few were collected until mid-October, each year. In the general patterns of seasonal prevalence, Ctritaeniorhynchus was first collected in June between 8th and 23th, and trapped in large numbers during the period from late July to late August, and showed a simple sharply pointed one-peaked curve while, C.pipiens pallens was found to be active through almost the entire season showing irregular curves with several peaks. The average number of A.sinensis in July rapidly decreased after 1992, and the number became particular low in 1994. The number of C.tritaeniorhynchus in August was 164.1 per trap-night in 1992, but in 1993 decreased abruptly to 46.1, and then increased to 689.4 in 1993. The total number of Cpipiens pallens progressively decreased during the initial 3 years from 1992, followed by a increase. A marked decrease on MPI was obtained in 1994. In the trend of nocturnal activities of C.pipiens pallens, with oncoming darkness they become very active, gradually decreasing in activity toward mid-night, but slightly increasing toward dawn, while, C.tritaeniorhynchus and A.sinensis were rather constantly active all through the night with more or less inconspicuous peaks twice a night. 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 total number of larval C.tritaeniorhynchus in rice paddies was highest in mid-August, and its number progressively decreased in early September because of insecticide spray. After late September, the larval mosquitoes were rarely found until rice plants were harvested. The larval C.tritaeniorhynchus and C.pipiens pallens showed high resistance levels and resistance ratios against 5 kinds of organophosphorus compounds, but low resistance against 2 synthetic pyrethroides. The present results indicated that the population density of A.sinensis and C.pipiens pallens in Kyungpook Province were decreasing over the four years from 1992 to 1995, while, C.tritaeniorhynchus was progressively increasing after 1993.