Abstract
The chironomid faunae in slow sand filter beds of filtration plants were investigated and compared between southwestern Japan, i.e., the Sakishima Islands (Ishigaki and Miyako Islands), and a plateau area, i.e., Honshu Island (Nagano Prefecture). As a result, the midge fauna was found to be dominated by two species (in order of abundance), Polypedilum nubifer (Skuse) and Cricotopus trifasciatus (Panzer) at Someya filtration plant in Nagano Prefecture. On the other hand, in the Ishigaki filtration plant, the most abundant species was Hanochironomus tumerestylus Ree, followed by P. nubifer which was also collected at Nagano Prefecture. Moreover, in Sodeyama filtration plant located in Miyako Island, the most abundant species was Cryptochironomus javae Kieffer, followed by Polypedilum nodosum (Johannsen). P. nubifer, Cricotopus bicinctus (Meigen) and Ablabesmyia moniliformis Fittkau were common species in all plants. The most important factor influencing the abundance of chironomid fauna supposedly is the water temperature in the slow sand filter beds.
