南方定点観測船に飛来した昆虫類 : 第 4 報特に蜻蛉類に関する観察

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1. During the service of the weather ship "Ojika" from July 25 to Aug. 9 at the Ocean Weather Station "Tango" 29°N 135°E, on the western Pacific one of the authors, Hashimoto, was on board the ship and observed the dragonflies visited the ship. 2. The following four species of the Odonata were recognized and captured during this period : Pantala flavescens ♂♂♀♀, Tramea virginia 10♂7♀, Anax parthenope julius 1♂2♀ and Anax guttatus 1♀. These were not teneral, being fed considerably before exodus, but their crops were, when dissected, quite empty. 3. The dragonflies came to the ship only when the constant southwestern wind prevails regardlesed of the wind velocity which fluctuated from 1 m/s to 11 m/s during July 28 to Aug. 4. No correlation was found between the number of the dragonflies encountered and the wind velocity. This would mean that the wind direction is the most leading meterological factor during this season. 4. When a dragonfly reaches the ship from the windward side it passes beyond the ship but remains for a certain minutes patrolling in the air-space just below the wind route which is to the opposite side of the ship. The time length and the size of the patrolling area depend on the wind velocity, the smaller the wind velocity the longer the patrol time and the greater the patrol size. 5. The dragonflies are readily attracted by the lights of the ship in the night, which is an unusual phenomenon on the land, but this was never seen in moonlight nights. The number of such night flight is much less than those comming in daytime. 6. Throughout a flight period more than several dozens of Pantala flavescens visited the ship every day. This suggests a large number of this dragonfly would pass over the sea during the same time. 7. The exodus site of them seems to be somewhere in southwestern direction if considered from the wind route and the known distributional range of these dragonflies. The occasional occurrence of some non-Japanese southern dragonflies such as, Anax guttatus, Tramea transmarina (probably including T. virginia), Tholymis tillarga, can be explained as rather regular transoceanic migrants from the southern countries.
日本昆虫学会の論文
1969-09-20

南方定点観測船に飛来した昆虫類 : 第 4 報特に蜻蛉類に関する観察

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