Gas Exchange in Aquatic Insects

Perhaps not surprisingly, in view of the rapid rate at which gases can diffuse within it, a gas-filled tracheal system has been retained by almost all aquatic forms in their evolution from terrestrial ancestors. Only rarely, for example, in the early larval stages of Chironomus and Simulium (Diptera), and Acentropus (Lepidoptera), is the system filled with liquid.

Oxygen may enter the tracheal system in gaseous form, that is, via functional spiracles (the "open" tracheal system) or may pass, in solution, directly across the body wall to the tracheal system, in which arrangement the spiracles are sealed (non-functional), and the tracheal system is said to be "closed." Aquatic insects with open tracheal systems exchange the gas within the system by periodically visiting the water surface, by obtaining gas from gas-filled spaces in aquatic plants, or through the use of a "gas gill" (a bubble or film of air that covers the spiracles, in to or out of which oxygen and carbon dioxide, respectively, can diffuse from/to the surrounding water). A significant amount of gas exchange may occur by direct diffusion across the body surface (cutaneous respiration) in larvae with an open system whose integument is thin, for example, mosquito larvae. Cutaneous respiration may entirely satisfy the requirements of insects with closed tracheal systems. However, in many species supplementary respiratory surfaces, "tracheal gills," have evolved, though these often become important only under oxygen-deficient conditions.

4.1. Closed Tracheal Systems

For small aquatic insects or those with a low metabolic rate, diffusion of gases across the body wall provides an adequate means of obtaining oxygen and excreting carbon dioxide.

480 In larger and/or more active forms, all or part of the body wall has a very thin cuticle and becomes richly tracheated to facilitate rapid entry and exit of gases from the tracheal system.

Beekeeping for Beginners

Beekeeping for Beginners

The information in this book is useful to anyone wanting to start beekeeping as a hobby or a business. It was written for beginners. Those who have never looked into beekeeping, may not understand the meaning of the terminology used by people in the industry. We have tried to overcome the problem by giving explanations. We want you to be able to use this book as a guide in to beekeeping.

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