Ecological studies on the black flies, Simulium aokii Takahasi, 1941 : (Studies on Black Fly.4)

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  • アオキツメトゲブユの分布及び習性について : (ブユの資料 4)
  • ブユの資料-4-
  • ブユ ノ シリョウ 4

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Abstract

1. Simulium aokii Takahasi, 1941 (possibly the synonym of S. oitana) is one of the commonest blackflies in Japan which seriously attack humans. In the present paper, the distribution and behavior of this species observed by the author and his colleagues are reported. 2. Eggs, larvae and pupae of this species were found abundantly in lowland streams such as irrigation ditches. They were occasionally collected in mountain streams of Honshu and Kyushu. 3. The oviposition of the females were made in the evening on wet substrates on or near the stream surface. The author observed, for example, that in 70 minutes 16 females deposited their eggs side by side in a large mass, finally attained to about 0.7cm wide and about 4cm long, on the surface of a wet blade of the aquatic plant (Sparganium ramosum), one of their most typical ovipositing substrates. While a few females laying eggs on their favorite substrates, the others were flying around to wait for their turn. An egg mass which was oviposited by a female consisted of 150-300 eggs. The eggs required about 10 days to hatch in the laboratory in March, under the room temperature of 8-16℃ at noon. 4. The larvae were found most abundantly in clear lowland streams of 1 to 0.3m wide and under the flowing velocity of 10 to 30m per minute. 5. In nature, the larvae prefer to attach on the tip of the lower surface of long tapering leaves less than 10cm below the water surface. However, the main facter in the choice of their habitat is not the kind of substrates, but their environmental conditions stated above. 6. The larvae being sedentary in its habitat on the favorable conditions, but they frequently change their position by looping-movements and by hanging with a fine silk thread which is secreted from the salivary slit. 7. The flight range of the females were observed in biting experiments on humans set in positions of every 100 meters from their closest breeding streams. The maximum number was seen right close the stream, but a few were collected up to the most distant site of 1, 000m. 8. Their seasonal occurrence was observed by collections at least once a month all through the year. The biting activities were found over the year, but were most serious from May to July. 9. The host preference for human, horse, cattle and goat was experimented. This species was found to be mainly attracted to human. Only a few specimens have so far been collected from cattle or horse.

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