富山県におけるコガタアカイエカ捕集数の年変動と殺虫剤抵抗性の関係

Abstract

In an attempt to predict the epidemic incidence of Japanese encephalitis in human population, a long-term surveillance on Culex tritaeniorhynchus, the vector of Japanese encephalitis virus, has been carried out at several observation stations in Toyama Prefecture since 1969. The numbers of the mosquito captured by the light trap had been decreasing since 1965 until 1977,and then began to reverse from 1978. This increasing trend appeared clear in 1982,although some decreases in the numbers were observed in 1984,1986 and 1988 in comparison with the previous years. The major cause of increase in the numbers of the mosquito may be attributed to the acquisition of insecticide resistance. Aerospray of agricultural pesticides or fungicides may not inhibit the appearance of the mosquito. In fact, the resistant/sensitive ratios for fenthion, fenitrothion and malathion of a resistant strain of C. tritaeniorhynchus, established in Toyama Prefecture, were 6,557,5,272 and 2,454,respectively. In an exposure experiment with the pesticide aerospray over a paddy field lethalities ranging from 7.6 to 71.6% were observed with the resistant strain of C. tritaeniorhynchus; these percentages could not be compared with the complete death of a sensitive strain.