Periodic emergence in some North European chironomids

Summary

In a brackish-water area near the Zoological Station of Tvärminne, S. Finland, pupal emergence of Chironomus halophilus, Microtendipes pedellus, Polypedilum nubeculosum, Limnochironomus nervosus, Lenzia flavipes, Tanytarsus heusdensis and Monotanytarsus inopertus occurred practically only around midnight, whilst in Allochironomus crassiforceps, Cladotanytarsus mancus and C. atridorsum small numbers of individuals emerged at other times also. A time difference was observed between the emergence bursts of the June and August generations of C. halophilus, M. pedellus, P. nubeculosum, L. flavipes, T. heusdensis and M. inopertus, the emergence burst being about 2 hrs. earlier in August than in June. It is concluded that the timing mechanism governing emergence is regulated by the day-to-night change in illumination. As the periodicity of emergence remained unchanged under rather different temperature conditions, it is concluded that the periodicity is temperature-independent, at least within ecological limits. In Allochironomus crassiforceps the emergence rhythm persists in darkness for at least 6 days. In the same species, the bulk of the males emerges within the first two-hour period of each peak and the females during the second peak, whilst in other species no differences could be observed in the time of emergence of the two sexes.