Akira Takai

Study on Methods for Estimating the Number of the Overwintering Green Rice Leafhopper, Nephotettix cincticeps UHLER (Hemiptera: Deltocephalidae) and their Population Dynamics

ツマグロヨコバイ越冬幼虫個体数の変動とその調査法について検討した。越冬幼虫の個体数調査法としてワク内すい取り法を用い,時間単位採集法を併用した。越冬世代の卵およびふ化直後の幼虫の死亡には,気温の影響が大きく働らいていると考えられる。各年および各調査地区とも越冬幼虫の主要な死亡時期は12月から1月上旬であった。越冬後の幼虫の令構成は4令が主体であった。越冬幼虫の個体数調査法である吹き飛ばし法の採集効率は20∼50%で,ワク内すい取り法にくらべて採集効率が低く,また採集時の気温が大きく関与していた。冬季間においてもクモ類はツマグロヨコバイの捕食者として重要な位置にあると推定された。

The estimation of population density of the green rice leafhopper,Nephotettix cinticeps Uhler, in spring field by the capture recapture method

The population parameters of green rice leafhopper,Nephotettix cincticeps in hibernated generation was estimated by the capture-recapture method on the gramineous weeds of resting paddy field from late in April to mid-May, 1962–1965. The difficulty of applying the capture-recapture method to this insect is caused from the low density and the low activity of the leafhopper, so that it is necessary to make the suitable plan of capture-recapture series and to construct the special method to detect the population parameters. The number of adults differed greatly among the years and among the plots in the same year. But, in general, the density was relatively high late in April, and decreased rapidly in May. The number of males was higher than that of females late in April, but decreased rapidly to become lower in May. The sampling efficiency with sweep-net depends upon the many factors, such as weather and floristic conditions; especially the atmospheric temperature and the force of wind are considered to affect greatly to the efficiency. In general, low temperature and strong wind are the cause of low sampling efficiency.