Field study on acoustic response of chironomid midges (Diptera: Chironomidae) around a hyper-eutrophic lake in Japan

A new method was developed to control adult chironomid midges, Chironomus plumosus (L.) and Einfeldia dissidens (Walker),using their acoustic responses to sound laps in the field. Trials were conducted in 1999 from 2 to 7 June (during emergence period of E. dissidens) and from 2 to 7 September (emergence period of C. plumosus) near hyper-eutrophic Lake Suwa in central Japan. Swarms of E. dissidens were formed at 1-3 m above the terrain and were observed from 1900 to 1930 hours. More than 97% of E. dissidens trapped from the swarms were males. In cylindrical sound traps, optimal trapping of swarming males occurred at a frequency of 240 Hz at 21.9 +/- 2.3 degreesC. Swarms of C. plumosus were formed at 1 m to >5 m above ground, and were observed from 1830 to 1900 hours. More than 88% of C, plumosus caught from the swarm were males, and optimal trapping of swarming males occurred at frequencies of 300-360 Hz at 20.7 +/- 0.5 degreesC. We compared our results with those of other chironomid species and attempted to clarify the relationship between female wing length and ambient ail temperature. There was no correlation between the most attractive frequency and female wing length. However, a positive correlation existed between the most attractive frequency and air temperature. It is concluded that the most attractive frequency differed among species (Interspecific) according to air temperature. These mechanisms may play an important role in isolation during chironomid swarming.