Diapause induction in the third and fourth instar of Chironomus riparius (Diptera) from Belgian lowland brooks
Goddeeris, Boudewijn; Vermeulen, Angelo C.; de Geest, Els; Jacobs, Herwig; Baert, Berten; Ollevier, Frans
published: Jan 11, 2001
ArtNo. ESP141015002007, Price: 29.00 €
Diapause in IVth instar larvae linked to overwintering conditions is a wellknown phenomenon in Chironomus species. Here, diapause induction in the IVth instar of Chironomus riparius MEeigen, 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 °C. 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. In long-day conditions of 16 h light per day at 15 °C, development is continuous: no diapause was observed. Furthermore, a desynchronisation between moulting and development of the imaginal discs was observed. In all experiments, as well as in the field, the development of the imaginal discs definitely began in the IIIrd instar: phases described in the literature for the early IVth instar have been observed in the IIIrd instar.