水ガメ内に産卵されるアカイエカの卵舟数の時間的並びに季節的消長
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Examinations were carried out for the hourly and seasonal distribution of the number of egg rafts of Culex pipiens pallens, laid on the rice-straw infusion in earthen jars which were set at ten different places in the campus of Nagasaki University School of Medicine. For the hourly distribution, egg rafts each in ten jars were counted every one hour from 6 PM to 7 AM for three days from July 20, 1964. For the seasonal distribution, the egg rafts were counted every day, each in 3 jars during the period from April 11 to December 31 in 1963 and in 2 jars during from February 1 to December 31 in 1964. The results obtained are summarized as follows: Hourly, the oviposition activity is in general the most active for one or two hours after sunset with a high peak at 8-9 PM, decreasing gradually towards the time several hours after midnight, becoming a little active again towards sunrise, showing that the activity seems to be controlled by the change in light. The results of hourly collections of egg rafts in 10 jars for 3 days in summer revealed that the number of egg rafts varied greatly with the sites where the jars were placed as shown by the figures given in circles in the order of small to large in Fig.1. The sites with greater number were places which were less windy and had something probably attractive to the gravid females such as residue of waste food for mosquito larvae sunk into a ditch. Seasonally, the oviposition took place from early February through late December. The oviposition activity becomes higher on May reaching the highest period covering from June to September, decreasing thereafter towards the end of the year. The higher activities observed in 1964 in the spring and on September and October than in 1963 seems to be due to the higher air temperatures on those days in 1964. At the most active period, the activity was higher in 1963 than in 1964 owing probably to the adequate amount of rainfall in the former and to the heavy drought especially in mid and late summer in the latter. The alternate rise and fall in the activity observed throughout the years appear to be roughly periodical and this may be due to the succession of generation in the mosquito population at outskirts of the campus.アカイエカの産卵活動の時間的並びに季節的消長を知るために,長崎大学医学部構内の条件の違った色々な場所に,ワラの煮汁を入れた水ガメを置いて,毎日産みつけられる卵舟を採集した.時間的消長の調査は1964年7月29日から3日間,10個の水ガメを使って,夕方から翌朝迄一時間毎に行った.季節的消長を調べるための卵舟の採集は,1963年には4月11日から3ケ所で12月31日迄,1964年には2月1日から2ケ所で年末迄続けた.1.産卵舟数の時間的消長は,場所により,日によって,かなり違っているが,一般的には日入後の8～9時を頂点とする旺盛な活動が見られ,日出頃にもしばしば活動の小山が認められる.このことから本種♀の産卵活動は明るさの変化と関係があるように思われる.2.産卵舟数はカメの設置場所によって,著しい変異が見られ,多少共,誘引源のあると思われる所で而も風当りの強くない所に多い傾向が認められる.3.季節的にみると,産卵は2月上旬から12月上旬まで行なわれるが,その活動は5月から次第に活発となり,6月から9月にかけて,最も盛んとなる.その後次第に減少する.1964年の春さきと秋の産卵活動が前年より活発であったのは,この時期の気温が比較的高かったことによると思われ,逆に夏期にはかなり低かったのは,この年の夏期の無雨と水不足によるように思われる.一年を通じて消長曲線をみると,両年共に,かなり規則正しい増減が繰り返されているが,このことは,あるいは,本医学部の周辺の住宅地でのアカイエカ個体群の世代の遷移と関係のある事ではないかと思われる.