Dispersal of Culex tritaeniorhynchus larvae (Diptera, Culicidae) by Water Currents in Rice Fields

水田内の水流によるコガタアカイエカ幼虫の分散量を知るために,長崎に多い段丘水田地帯で調査をした.正常に水管理されている水田では,通常,取り入れ口から出口に向う細い流れが生じるだけで,そこから離れると水の動きはなくなった.しかし,そのような水田でも,コガタアカイエカ幼虫の流出量は非常に高い場合があり,1日あたり推定流出量の最大値は35.96%であった.従って,豪雨や長雨によって水田が氾濫した場合には,コガタアカイエカ幼虫個体群は懐滅的な影響を受けると予想される.この推測を裏づける一観察例を紹介した.これらの結果にもとづき,水田に発生する蚊に対する水流の影響を個体群動態や防除法と関連づけて論じた.また蚊幼虫の分散の意義についても,発生場所のタイプごとに考察した.Influence of water currents on the dispersal of Culex tritaeniorhynchus larvae was studied in a terraced rice field area common in the Nagasaki district, Japan. In rice fields under normal water regulation, water was stagnant except a route connecting the inlet and the outlet. However, emigration rates of tritaeniorhynchus larvae from these rice fields were sometimes very high, the maximum estimate being 0.3596 per day. This strongly suggests the passible destructive effect of heavy and/or successive rains on tritaeniorhynchus populations in rice fields, especially in terraced ones. An observation to support this was presented. Various aspects of the effect of water currents on mosquitoes in rice fields were discussed in relation to population dynamics and control. Also, significance of larval dispersal was examined in relation to various types of breeding habitats of mosquitoes