Seasonal trends in populations of chironomid midges in the high mountain Nishina Three Lakes in Japan

Chironomidae, one of the largest groups of aquatic insects, occur in most types of freshwater habitats such as springs, streams and seepage areas, rivers, lakes, ponds, marshes, and temporary pools (CRANSTON 1995}. Approximately 5000 species have been described world-wide (CRANSTON & MARTIN 1989). About l 000 species are known from Japan (SASA & KIKUCHI 1995), but few studies on chironomid fauna in lentic/lotic habitats have been undertaken in Japan because of the difficulty of larval species identification. Lake Aoki (36°37'N; 137°5l'E), Nakatsuna (36°36'N; 137°5l'E), and Kizaki (36°33'N; 137°50'E) are called the Nishina Three Lakes and are connected by the same water system, the Nougu River (Fig. 1). Lake Aoki (surface area 1.86 km, altitude 822 m a.s.l., maximum depth 58.0 m) is the deepest and has the greatest water volume. Lake Nakatsuna