コガタアカイエカの群飛についての予報

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Investigations on the swarm of Culex tritaeniorhynchus were carried out in the field in villages around Nagasaki and Isahaya Cities during from early spring through late autumn in 1965 and 1966. The swarms were ellipsoid, typically about 0.7×1.0-1.5m, in shape, and formed in the air at about 1.5m height, usually obliquely and sometimes right above the swells of grasses or shrubs; frequently by the dry ice traps; and sometimes under the eaves of animal sheds as shown in Figs.1 and 2. A swarm started usually at about sun-set and progressed through an increasing phase for 10 minutes, to a prosperous phase for some 15 minutes when the swarm contained one to two hundred males, and through a decreasing phase for some ten minutes they disappeared as shown in Fig.3. The starting time of the swarm was roughly parallel with the sunset time during the periods from April to June and after mid-October, while in from July to September the starting time became late by 10 to 15 minutes (Fig.4). When compared the seasonal prevalence of the population density in the swarms (males) which were found within a definite area and that of females which were found in a pig-shed, it was found that: In May and April, hibernated females were only found; from the end of April through the end of August the two prevalence curves passed over roughly in parallel; while, on September a sudden and great fall in the density of females took place and thereafter, in spite of near absence of females, the males continued to swarm till the beginning of November (Fig.5). The female rate to the total number of mosquitoes found in the typical swarm usually formed in the field was roughly 2.3% in an average and 9.1% in a maximal case. The rate was as high as 14.3% for average and 25.7% for maximum in the swarm formed by the dry ice traps probably owing to the joining to the swarm of the females which were attracted to CO_2 gas. The rate was intermediate between the above two in the case of the swarm formed under the eaves of animal-sheds. Seasonally, the rate was higher during the active feeding season of the mosquito than in those days when females had entered hibernation. During the process of swarming, the rate became higher in the decreasing phase owing to the gradual disappearing of males (Table 1). The swarm was formed at down, though for a shorter period and in a smaller scale than those formed in the evening. Within the swarm of this mosquito, mosquitoes of seven other species were found in a rare cases and in a very small numbers. The swarming of C. tritaeniorhynchus is considered to be closely related to the mating as mating is very frequently observed within the swarm.1. 1965, 1966年の早春から晩秋にかけて,長崎・諫早両市近郊の,数部落の水田地帯で,コガタアカイエカの群飛についての観察調査をおこなった.2.たけの高い草株,石垣,灌木,畜舎の軒先,水田わきに設置したドライアイストラップなどのように,周囲から一段と高く突出した物体の上または斜め上に,地上約1.5mの空間に,0.7×1.0～1.5mの楕円体として群飛の形成されることが多い.3.群飛は,一般に5-10個体に始まり,以後約10分間の段階的に増加する増加期,ふつう約100～200個体からなる15分間くらいの最盛期,約10分間の段階的な数の減少を示す減少期を経て解散に至る.4.群飛が,最初にみられた4月下旬から,最後にみられた11月下旬までを通じて,群飛の開始時刻は,大体においては日没時刻の季節的変化と平行的であるが,季節による歪みもみられる.すなわち,4～6月には群飛は日没頃に始まるが,7～9月には10～15分も遅く始まり,10月中旬以降は再び日没頃に開始される.5.一定方法で観察した群飛の,♂の個体群密度の季節的消長と,豚舎で定期的に採集した♀のそれとを比較すると,3～4月には越年♀だけが採集され,4月末新生成虫の発生以後は,♂と♀とはほぼ平行的に消長するが,9月に入ると♀は急激に減少しほとんど採れなくなる.しかし♂は9月にはなお盛んに活動しており,10月においてさえかなり活動して11月上旬まで続く.♀が越年に入ると思われる9月上旬以後,♂の群飛がなお11月上旬まで続いて観察されることは極めて興味のあることである.6.群飛中に見出だされる♀の割合については,時期により場所によって調査回数がまちまちであり非常に少ない場合もあるので,決定的な結論は下し得ないが,定期的な野外での群飛の場合には,最高9.1%,平均的には約2.3%であるが,♀を誘引するために設置したドライアイストラップ付近でのものでは最高25.7%,平均的には約14.3%と非常に高い.畜舎付近でみられるものでは,♀の比率がそれらあ中間にくる.季節的にみると,蚊の発生が盛んな時期に高く,10月以後は極めて低くなる.時間的には,群飛の減少期に特に高くなる傾向がみられる.7.朝方,日の出前約30分から,12～15分位のあいだ,小規模で継続時間の短かい群飛の生じることを確認した.8.本種の群飛中には,他の7種の蚊が採集されたが,そのような例は比較的稀であり,個体数も極めて少ない.

コガタアカイエカの群飛についての予報

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