Report on Drosophila melanogaster larvae without functional tracheae

A network of tubes, the tracheal system, ensures circulation of oxygen and carbon dioxide in insects. A stabilizing chitinous cuticle lines this ectodermal tissue that commonly fills with gas shortly before hatching. In this study, we report on Drosophila melanogaster larvae that lack a functional tracheal system through the reduction of the expression of the cuticle gene kkv or snsl by specific RNA interference in tracheal cells of the embryo. These embryos complete development and hatch arguing that functional tracheae are not required for embryogenesis. After hatching, larvae with dysfunctional tracheae ingest only little food and grow slowly. Without attaining the critical size for stage transition, a few of them moult to the next larval stage. We further show that hypoxia is induced in these larvae that conceptually switch to skin respiration. The rescue response is, however, futile and the respective larvae die latest after 4 days. Hence, a small body size and skin respiration per se are insufficient to ensure survival. Based on our data, we hypothesize that a low oxygen concentration entails a conflict between the developmental progress and a protective programme destined to restrict growth under hypoxia. D.melanogaster larvae with dysfunctional tracheae will be useful to identify those factors accounting for the impact of respiration on growth and development ultimately allowing understanding these aspects of insect ecology.