Diapause induction in the third and fourth instar of Chironomus riparius (Diptera) from Belgian lowland brooks
Goddeeris, BR × Vermeulen, AC De Geest, E Jacobs, H Baert, B Ollevier, Frans #
E schweizerbartsche verlags
Archiv für Hydrobiologie vol:150 issue:2 pages:307-327
Diapause in IVth instar larvae linked to overwintering conditions is a well-known phenomenon in Chironomus species. Here, diapause induction in the IVth instar of Chironomus riparius MEIGEN, 1804, is described for the first time from a combination of field and laboratory research. These observations are relevant for understanding the ecology of Ch. riparius, a widespread species in Europe, and for its use as a bioindicator in water and sediment quality assessment. This diapause is linked to overwintering and is characterised by an arrest in phase IV4-5a of the development of the imaginal discs in the last larval instar. The diapause could be induced experimentally by short-day conditions, i.e, a photoperiod of 8 hours light per day at 15 degreesC. However, there was a great variation in the diapause response. Under short-day conditions, half of the larvae went into a long-lasting diapause while the other half continued their development after a much shorter diapause. Moreover, diapause effects on the size of IVth instar larvae have been examined. The IIIrd instar also appears to be affected by this overwintering diapause, causing a retardation of the moult to the IVth instar. Diapause phenomena in the IIIrd instar of Chironomus species have never been described before.