Life cycles and population dynamics

Abstract

As insects belonging to the Endopterygota (or Holometabola), the life cycle of Chironomidae is divided into four distinct stages, i.e. egg, larva, pupa and imago. Notwithstanding the large number of species within the family, chironomids share one conspicuous life history characteristic in that the last two stages are generally very short in duration, while the lengths of egg and larval stages vary substantially between and within species. This seems to be related to the fact that, as in some other aquatic insect orders such as the Ephemeroptera and Plecoptera, chironomid adults mostly rely upon the energy stored during the larval stage to accomplish reproduction, the single most important task assigned to them. Though feeding is known to occur in adults (Chapter 9), this constitutes a tiny proportion of energy acquisition and does not contribute significantly to overall reproductive output, a situation which is clearly different from that of many other related dipterans such as blood-sucking blackflies and mosquitoes. Clear demarcation of energy acquisition and reproduction along the phases of metamorphosis implies that the adult, reproductive phase is heavily dependent on the preceding feeding phase. If a fixed amount of energy is to be allocated to the maintenance of the adult body and gamete production, the highest reproductive output would be achieved by minimizing the length of the adult stage, the strategy that seems to have been adopted by the vast majority of chironomid species.