Studies on the effectiveness of the Guppy Poecilia reticulata in controlling Culex pipiens s.l. : Part II. Efficiency of predation in breeding habitats

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  • アカイエカ発生源対策におけるグッピー Poecilia reticulata 利用の基礎的研究 : 第 2 報発生源での捕食の効率
  • 発生源での捕食の効率
  • ハッセイ ゲン デ ノ ホショク ノ コウリツ

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Experiments were carried out with two guppies in each of 200 liter tanks placed outdoors under natural summer condition of Tokyo; water temperature was around 25-27℃. There was a control tank for each of the above experimental tanks. Five egg rafts of Culex pipiens pallens were given each morning for seven days. Each egg raft contained an average of 249 eggs. It was observed that guppies pecked at and ate the rafts; the number eaten was estimated at three rafts per day. Some of the larvae had hatched from the eggs, but it was difficult to estimate the number which did because of their small size. In any case, no larvae were found on the eighth morning. In order to determine the number of larvae of different developmental stages which was eaten per day, various stage of larvae were introduced in each tank. When 2,000 larvae, which had recently hatched from egg were supplied, it was noted that 369 of them had pupated after six to ten days. In the control tank wherein there were no guppies 1,614 larvae survived and pupated. It was estimated that 386 of the original 2,000 larvae in the control tank died naturally. If one assumes that an approximately equal number of larvae will die naturally in the experimental tank, then the actual number of larvae consumed was estimated at 1,245,or (2,000-369)-(2,000-1,614), during the larval period. When 500 larvae of age three days after hatching were supplied in the same way as mentioned above, the number of larvae eaten was estimated at 249 larvae by the end of the pupation period; under similar conditions, 142 four-day larvae were consumed; 50 five-day larvae; and 35 six-day were eaten. From the above the number of larvae eaten per day was calculated in the case of 0 to two days old larvae as : (1245-249)/3=332 larvae. In the same way, 107 three-day old larvae, 92 four-day old and 15 five-day old larvae were eaten per day. When a mixed-age population of larvae were supplied, the number eaten was greater in younger-aged larvae than older ones. However, some older ones were always eaten in spite of the presence of young larvae still remaining in the tank, although the number of older larvae consumed was less in comparison when a homogeneous age-group population was available.

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