1998 年 48 巻 1 号 p. 27-36
As a part of a research program on the ecology of odonate larvae inhabiting artificial ponds, we surveyed outdoor swimming pools of primary schools in Kyoto City every late spring. During a 4 year period, 11 species of odonate larvae (Libellulidae, Aeshnidae, Gomphidae and Coenagrionidae: 7, 1, 1 and 2 species, respectively) were collected. Only larval Sympetrum striolatum imitoides predominated at most swimming pools. We took samples from 4 schools every late spring for 4 years and obtained the annual changes in the numbers of their larvae. This survey revealed that while larval S. striolatum imitoides was common in the school pools in Kyoto City, density varied from year to year. To clarify why only larvae of S. striolatum imitoides were dominant in the pools, their life cycle was examined at one pool. Larvae of chironomids, mayflies (Cloeon dipterum), water bug (Anisops ogasawarensis) and diving beetles as well as larval S. striolatum imitoides coexisted among detritus on the bottom. Especially chironomid larvae, which are preferred by larval S. striolatum imitoides, were present at high density. Most eggs of S. striolatum imitoides laid in Autumn hatched by mid winter, then the larvae rearched the final instar in late May. We estimeated that one third of them became adult before mid June, when the water was drained for pool-cleaning. As a reason for the dominance of larval S. striolatum imitoides, the following three traits may have been responsible: (i) their life cycle coincides with the off-season for the pool, (ii) females oviposit directly into the water, and (iii) larval S. striolatum imitoides prey on smaller larvae of other species of dragonflies because their eggs hatch earlier than other species.