Respiration

Abstract

The form and function of the cyclorrhaphan respiratory system is dealt with in this chapter. Externally, the main components are larval anterior and posterior spiracles and, in the pupa, pupal spiracles. These three spiracles are each diverse in form and features and are a source of taxonomic and character data. Experiments blocking artificially the spiracles demonstrate their importance for respiration. Oxygen permeating through thin body walls also occurs and is probably important in the first and second stages and endoparasitic larvae. Larval and pupal spiracles are permanently open, but they can sometimes be folded into creases or withdrawn into pockets of the body wall which shuts them off from the atmosphere. Anterior spiracles are a minor component of larval respiration, but will take over if the posterior spiracles become damaged. In contrast, they are important for pupal respiration as a route for gaseous exchange in and out of an open space at the front of the puparium. The posterior spiracles are most important for larval respiration. In aquatic larvae, the anal segment is often extended which enables the larva to project the posterior spiracles while remaining submerged. An extreme form of extension occurs in larvae that have folded anal segments. When the anal segments unfold, the anal segment can reach several times the body length and correlated with extensions to the breathing tubes, enables these larvae to survive at greater depth than larvae lacking these features. Endoparasitic larvae possess specialised mechanisms for accessing air from inside hosts. The influence of respiration on feeding and locomotion and vice versa is also considered.