Seasonal Migrations and Age Structure of Adults of Two Dryomyzid Species (Diptera, Dryomyzidae) in Central Japan

Using attracting traps baited with fermenting bananas, dryomyzid flies were collected at twelve altitudinally different points (from 500 to 2, 000 m above sea level) in Tobu-machi, Nagano Prefecture, in 1990. Two dryomyzid species, Dryomyza ecalcarata and D. melanacme, were common at higher altitudes than 630 m above sea level, and their active season was from May to November. However, appearance of these species in spring was delayed at higher trapping points. Flies of D. ecalcarata appearing in lowlands seemed to migrate to highlands in mid-summer, but they seemed to return to lowlands in autumn. In summer, D. melanacme also moved from lowlands to highlands, but its movement is categorized as dispersion because only a part of the lowland population moved to highlands. Age structure of females of these two species shows that start of breeding of D. melanacme was earlier than that of D. ecalcarata. This means that breeding season of D. melanacme was longer than that of D. ecalcarata.