Diel emergence patterns of lotic Chironomidae

SUMMARY. Six channels were constructed in various parts of two riffles from which chironomid exuviae were collected every 3 h for three 24-h periods in July 1974. Diel emergence patterns were calculated for twelve abundant species and six different patterns were observed.
Krenosmittia cf. camptopheleps and Cordites had their major emergence pulse during peak light periods and it is proposed that high or increasing light intensity is a cue for their emergence. Stempellinella cf. brevis begins its emergence in the morning and continues until after darkness. Increasing and high water temperatures are suggested as the emergence cue since emergence tracks water temperatures with little apparent effect of light. Parametriocnemus sp. and Polypedilum ( Tripodura ) sp. begin emerging in late evening and continue into early daylight hours. These patterns indicate low and decreasing water temperatures as the emergence cue with little apparent effect of light. Corynoneura sp. and Thienemanniella sp. emerged primarily during daylight hours with a minor pulse in the morning and the major pulse in late afternoon. It is proposed that the emergence cue is simply the presence of light and that water temperature determines how many individuals are able to prepare for emergence and respond to the cue. Rheotanytarsus cf. exiguus and Tanytarsus ( Sublettea ) coffmani have major emergence peaks just after sunset and minor pulses in the morning hours. Changes in light are proposed as their emergence cue with water temperatures determining the number of individuals able to respond to that cue. Eukiefferiella discoforipes gr. sp. and Nilotanypus sp. emerge continuously throughout daylight and darkness hours, showing no obvious pattern.