クスサン幼虫の集合性
スポンサーリンク
概要
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This species lays eggs in a mass and the hatched larvae have a strong tendency to form aggregation, though this habit diminishes gradually as development advances. In the present paper, the author intended to know the influence of larval aggregation on the mortality and the development and to discuss the mechanism of this influence. The rearing experiments were carried out under the condition of room temperature and natural daylength in May and June. The results obtained are summarized as follows: 1) Mortalities of the 1st and 2nd instar larvae decreased with the increase in the size of larval aggregation. 2) To determine a most susceptible period for aggregation effect, larvae were isolated or aggregated at the various larval stages. There was a critical period of the development for the larval aggregation during the period from the 7th to the 12th day after the hatching. 3) The larval aggregation mixed with different instars were set up experimentally and examined the interaction between them. When the old larvae were mixed with the 1st instars, the development of the 1st instars was protracted and the mortality became high. 4) Various sizes of larval aggregation were set up on the matured leaves as food. The mortality was reduced with the increase in the size of larval aggregation up to the 17th day after hatching. But finally, they all died out prior to the 1st moult due to hardiness of food enough to feed. 5) Up to the 11th day after hatching, young larvae have low ability to establish the aggregation within a day, when the aggregated larvae were isolated singly. The frequency of larvae establishing aggregation increased gradually after this time. 6) There was no consistent relationship between the size of egg mass and the synchronism of hatching from a. mass. It takes 2 or 3 days for the completion of hatching from an egg mass and the larvae tend to form their aggregation in each day. 7) Formation of larval aggregation is due to the silk trail from newly hatched larvae. In the present species, there was a striking effects of aggregation on the larval mortality and the larval development. These effects of aggregation should be due to mutual stimulation of larvae and the mechanism of the effects is similar to the so-called "effet de groupe" according to Chauvin.
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