[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. 3. Some experimental trials for control of nuisance midges and proposed counterplans].

In the present paper the author tried to forecast the massive emergence of adult Tokunagayusurika akamusi midges from Lake Suwa. Furthermore, several control measures for chironomids were examined. The results obtained are as follows: 1. The forecast for the emergence of adult midges from the lake. A survey of the chironomid larva population was carried out at three stations in the lake. T. akamusi emerged at about the tenth day after the decrease of the larval number and at this time the temperature of the bottom water was within the range of 11-18 degrees C. The flights of adult midges were closely related to environmental factors such as air temperature, the strength and the direction of the wind and the light conditions. 2. The attraction of adult midges to lamps of various colors and wattages was studied. A comparative study on various colors of lights of the same intensity (100 W) showed that white was more attractive to chironomids than yellow, and that both colors were preferred to red, green, or blue. The experiment on light intensity showed that 100 W was more effective than 40 W and 20 W and that no differences in preference were observed between 100 W and 60 W white lamps. Therefore, the light intensity was thought to be more important than color for the control of adult midges. 3. Cyprinus is the natural enemy of the larva and pupae of T. akamusi. The total numbers of adult T. akamusi emerging from Enclosure A (in which there were 10 times as many Cyprinus as in the natural lake water), Enclosure B (no predator was present), and Station C (the natural lake) were 458, 1108, and 684 ind./m2, respectively. It was estimated that 38% of larvae or pupae were eaten by the fish in the lake, and by putting Cyprinus into the water, the percentage increased to 58%. It seems that Cyprinus has a significant effect in reducing the number of midges in field trials. 4. The control of T. akamusi may also be achieved by employing general prevention, by physical and biological means, depending upon the nature of the breeding source, and the cooperation of inhabitants and persons concerned is necessary to carry out the control of adult midges. 5. The proposals for the control of the nuisance caused by chironomid midges are as follows: (1) To make the inhabitants aware of the ecological role of chironomids in the lake, and the importance of protection of the natural ecosystem.(ABSTRACT TRUNCATED AT 400 WORDS)