The tracheal system is a system of gas-filled tubes that develops embryonically as a series of segmental invaginations of the integument. The invaginations anastomose and branch and eventually form tracheoles across which the vast majority of gas exchange occurs. The external openings of the tracheal system (spiracles) are generally equipped with valves, hairs, or sieve plates, whose primary function is probably prevention of water loss.

Because oxygen can diffuse more rapidly in the gaseous state and is in higher concentration in air than in water, the requirements of most small insects and many large resting insects can be satisfied entirely by diffusion. Possibly to reduce water loss or as an adaptation to living in hypoxic or hypercapnic environments, some larger insects use a discontinuous gas exchange cycle (DGC). In DGC the spiracles are kept almost closed and carbon dioxide is temporarily stored, largely as bicarbonate in the hemolymph. As oxygen is used, a slight vacuum is created in the tracheal system that sucks in more air and reduces outward diffusion of water vapor. Periodically, the spiracular valves are opened for a short time when massive release of carbon dioxide occurs.

To increase the diffusion gradient between the tracheal system and tissues, many large insects ventilate the system by alternately increasing and decreasing its volume. Frequently the volume of tidal air moved during ventilation is increased through the development of large compressible air sacs, and by unidirectional air flow. Autoventilation, which relies on movements of the pterothorax during wing beating, occurs in many groups that have synchronous flight muscles.

Aquatic insects have either a closed tracheal system in which the spiracles are sealed or an open tracheal system with functional spiracles. In many insects with a closed tracheal system, cutaneous diffusion may entirely satisfy oxygen requirements. Accessory respiratory structures (tracheal gills) may be present though these are often important only under oxygen-deficient conditions. Some insects with open tracheal systems obtain oxygen by periodic visits to the water surface, or from air spaces in plants. Others hold a store of gas (gas gill) about their body. This may be either temporary, when an insect must visit the water surface to renew the oxygen content of the gill, or permanent (a plastron), when oxygen is renewed by diffusion into the gill from the surrounding medium.

For many endoparasitic insects, cutaneous diffusion is sufficientto satisfy requirements. In others there are special structural adaptations that ensure that the parasite remains in contact with atmospheric air.

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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