Mechanism of Massive Flights of Chironomid Midges (Diptera) and Plans for their Control in a Hyper-eutrophic Lake.

摘要

Chironomid midges emerging from eutrophic lakes have become intolerable because their high densities are a severe nuisance and cause economic problems. In this paper, we gave an outline of changes in the surrounding environment of chironomids in recent years and we examined the countermeasure for their control in Lake Suwa. Recent factors underlying the increasingly massive flights of midges from Lake Suwa to human living spaces were 1) humans invading the habitats of chironomid, causing human living space and those habitats to overlap (an increase in the intensity and number of lights around the lake drew many chironomid midges to human construction). 2) the progressive eutrophication of the lake provided chir- onomid larvae with a steady food supply so that the chironomid population density was maintained and stabilized. 3) fishes, which were the main predator of chironomid larvae, have decreased because the structure of the littoral zone was largely changed by human activity which destroyed their reproductive habitats. Basically, the control measures for chironomids in natural lakes were aimed mainly at stabilization of the lake ecosystem for the improvement of lake water quality and restoration of the littoral zone. A plan which effectively promotes the ideal of human coexistence with the organisms as auxiliary measures must be examined.