Biology of Chironomus kiiensis : (Diptera : Chironomidae)^*

Biological studies of Chironomus kiiensis Tokunaga (Diptera : Chironomidae), one of the dominant paddy dwelling chironomid species in the Yamaguchi area, were made in 1979 and 1980 both in the laboratory and paddy fields. Morphological studies including frequency distribution of head width indicated that number of larval instars in four, and the first instar larvae lack lateral and ventral tubules I and II, the second instar larvae lack lateral tubules, and the third and fourth instar larvae have all blood gills. The larvae made undulations in their nests making usually an antero-posterior current, and turned periodically to change their orientation. Strong phototaxis was seen in the first instar larvae. It was less sensitive in the second instar larvae, and there was none in the third and fourth instar larvae. Emergence peaks of adults occurred between 20 : 00 and 21 : 30, and no emergences were seen between sunrise and around 15 : 00. Adult males showed greater longevity than females. Longevity under the condition with food was greater than that without food, and under the condition at 15℃ was greater than that at 25℃. Developmental period from hatching to emergence took 15 days at 25℃. The period between egg and emergence is estimated as about 17-18 days. The highest peak in the number of specimens collected by the Malaise trap occurred in early July, and the number decreased accordingly. Judging from rearing experiments and the Malaise trap collectoions, it is estimated that there may be 6 generations from late May to early September when water is available.