Studies on the massive flights of chironomid midges (Diptera: Chironomidae) as nuisance insects and plans for their control in the Lake Suwa area, central Japan. 1. Occurrence of massive flights of Tokunagayusurika akamusi

Adult Chironomidae (Diptera, particularly Chironomus plumosus and Tokunagayusurika akamusi) emerging from eutrophic lakes or polluted bodies of water in Japan have become intolerable because they pose a severe nuisance and cause economic problems. In the Lake Suwa area, massive flights of adult midges of T. akamusi have occurred frequently, and caused problems in the daily life of local residents or for the tourist business. The author tried to clarify the biological and hygienic problems involved in these massive flights. In order to control adult midges, the distribution of larvae in the lake, the period and quantity of emergence from water, the time of flight, and the dispersal range of T. akamusi midges were studied. The results obtained are as follows: 1. Larvae of T. akamusi are distributed over the whole lake, especially in the east and southeast part with high densities. Mean biomass was about 100 g wet weight/m2 in Lake Suwa. On the shore near these areas, dense swarms of adult midges were found. 2. Emergence of T. akamusi from Lake Suwa was observed at the end of September and lasted till the middle of November. The emergence peaked in the middle of October. The time of flight was mainly at 17: 30-19: 30. 3. The dispersal ranges of adult midges were confirmed with two methods, i.e. the ordinary light trap method and a questionnaire survey of 544 residents. The result obtained with the questionnaire survey was consistent with that of the light trap method and the questionnaire survey made it possible to collect information in a wider area than the usual one. 4. T. akamusi midges reached areas over 3 km from the lake, but more than 90 percent of the midges flew within 500 m of the lake's shoreline. However, even in the more distant places where there was a source of bright light there were many adult midges. 5. The wind (at 18: 30) was the main factor which expanded the dispersal range of adults. We observed that many adults appeared after a strong wind (6-7 m/s). 6. Many adult midges were collected by light trap at the top of a building with a height of 45 meters.