コシアキトンボ Pseudothemis zonata (Burm.) の生活史の研究 : II 幼虫期
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During the period 1966-1968 the writer obtained informations on the life-history of Pseudothemis zonata (Burm.) to some extent from the field observation and the laboratory culture of the larvae. In the previous paper the ecology of the adult stage was reported as the first part of the work. This paper deals with the immature stage, with special account of external morphology, habits, habitat preferency and rate of larval development, based on the field and laboratory data. The laboratory culture was carried out using the container of polyethylene (15 cm×10 cm, 7 cm deep) with submerged decaying leaves collected from the pondbottom as the concealment for the larvae, and also as the source of food for early stage-larvae, since microorganisms such as Rotifer and Protozoa inhabit them. As the prey animals for grown larvae mud-worms (Annelida) were used. The results are summarized as follows : 1. Eggs hatch in 7 to 14 days or more. 2. The typical number of the instars are 12 (Figs. 1-5, Tab. 1). 3. The first instar larvae show negative phototaxis. Larvae from the 4th to the final (12th) instar cling to the under side of leaves or other debris during the daylight hours. 4. Larvae of the earlier instars are sometimes the victims of cannibalism, but the older instars seem to escape this fate. 5. A final instar larva attacked a pond snail larger than itself, and ate the epidermis of the foot. This is probably an exceptional behavior. 6. Seasonal migration from the summer habitat near the pond margin to a winter habitat, exact location of which has not been ascertained, occured in late autumn, while the reverse movement occured in late spring (Fig. 7). 7. Rates of larval development were similar, although the laboratory reared larvae were kept during the winter at a temperature appreciably above the pond temperature of the field larvae (Fig. 8). 8. The laboratory data show that there are two groups of larvae, univoltine and semivoltine. Individuals from eggs deposited early in the season are frequently univoltine, and those from eggs deposited later in the season are more frequently semivoltine (Fig. 8, Tab. 2). 9. The shortest duration of immature stage at 20-28℃ was calculated at 106 days based on the laboratory rearing. 10. If once the development of pterothoracic muscles commences, it induces molting without pause when the temperature is enough high.
- 1969-12-25
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