Life history of Sympetrum striolatum imitoides Bartenef at an outdoor swimming pool in an urban area (Anisoptera: Libellulidae)

Although natural odonate habitats have decreased recently due to disappearance of ponds from urban areas, it is shown that outdoor swimming pools during the off season become available as a habitat for some spp. Out of 24 swimming pools at primary schools in Kyoto city (Japan) examined during the period from late May to early June, late instar larvae of S. s. imitoides, S. frequens and S. darwinianum were found in 22 (92%), 9(42%) and 2(8%), resp. The life history of S. s. imitoides, the most common of these, was investigated at the swimming pool of one primary school. Larvae were distributed contagiously in detritus settling towards the periphery of the pool, and we estimated the number of last instar larvae in late May as ca 2000. There were numerous chironomid larvae in the pool which the larvae of S. s. imitoides consumed preferentially. Adult emergence was observed from the end of May but was interrupted due to poolcleaning. Mature dragonflies sought out the pool in Oct. and males established territories for 1-18 days. It is concluded, the reason why imitoides larvae are found so commonly at swimming pools is that, their life history pattern of laying eggs in Oct. with adult eclosion the next June coincides with the non-use period of the pools, and females lay eggs directly into the water.