Gas Exchange

segment 7

segment 3

main hemocoel compartment segment 9

tokus compartment

FIGURE 15.3. Tufts of tracheae in the eighth abdominal segment of Calpodes ethlius that perhaps serve to aerate hemocytes. Arrows indicate direction of hemolymph flow. [From M. Locke, 1998, Caterpillars have evolved lungs for hemocyte gas exchange, J. Insect Physiol. 44:1-20. With permission from Elsevier.]

In the smallest tracheoles, however, only the cuticulin envelope is present and, furthermore, this contains fine pores. These two features may be associated with movement of liquid into and out of tracheoles in connection with gas exchange (Section 3.1) (Locke, 1966).

2.2. Spiracles

Only in some apterygotes do tracheae originate at the body surface. Normally, they arise slightly below the body surface from which they are separated by a small cavity, the atrium (Figure 15.4A). In this arrangment, the term "spiracle" generally includes both the atrium and the spiracle sensu stricto, that is, the tracheal pore. Except for those of a few insects that live in humid microclimates, spiracles may be covered, for example, by the elytra or wings in Hemiptera and Coleoptera, or are equipped with various valves for prevention of water loss. The valves may take the form of one or more cuticular plates that can be pulled over a spiracle by means of a closer muscle (Figure l5.4B-D). Opening of the valve(s) is effected either by the natural elasticity of the surrounding cuticle or by an opener muscle. Alternatively, the valve may be a cuticular lever which by muscle action constricts the trachea adjacent to the atrium (Figure l5.4E,F). In lieu of, or in addition to, the valves, there may be hairs lining the atrium or a sieve plate (a cuticular pad penetrated by many fine pores) covering the atrial pore. It is commonly assumed that an important function of these hairs and sieve plates is to prevent dust entry. However, as Miller (1974) noted, sieve plates are not better developed on inspiratory than on expiratory spiracles and several other functions can be suggested: (1) they may prevent waterlogging of the tracheal system in terrestrial species during rain, in aquatic insects, and in species that live in moist soil, rotting

FIGURE 15.4. Spiracular structure. (A) Section through spiracle to show general arrangement; (B, C) outer and inner views of second thoracic spiracle of grasshopper; (D) diagrammatic section through spiracle to show mechanism of closure. The valve is opened by movement of the mesepimeron, closed by contraction of the muscle; (E) closing mechanism on flea trachea; and (F) section through flea trachea at level of closing mechanism. [A-C, from R. E. Snodgrass, Principles of Insect Morphology. Copyright 1935 by McGraw-Hill, Inc. Used with permission of McGraw-Hill Book Company. D, after P. L. Miller, 1960, Respiration in the desert locust. II. The control of the spiracles, J. Exp. Biol. 37:237-263. By permission of Cambridge University Press. E. F, after V. B. Wigglesworth, 1965, The Principles of Insect Physiology, 6th ed., Methuen and Co. By permission of the author.]

FIGURE 15.4. Spiracular structure. (A) Section through spiracle to show general arrangement; (B, C) outer and inner views of second thoracic spiracle of grasshopper; (D) diagrammatic section through spiracle to show mechanism of closure. The valve is opened by movement of the mesepimeron, closed by contraction of the muscle; (E) closing mechanism on flea trachea; and (F) section through flea trachea at level of closing mechanism. [A-C, from R. E. Snodgrass, Principles of Insect Morphology. Copyright 1935 by McGraw-Hill, Inc. Used with permission of McGraw-Hill Book Company. D, after P. L. Miller, 1960, Respiration in the desert locust. II. The control of the spiracles, J. Exp. Biol. 37:237-263. By permission of Cambridge University Press. E. F, after V. B. Wigglesworth, 1965, The Principles of Insect Physiology, 6th ed., Methuen and Co. By permission of the author.]

vegetation, etc.; (2) they may prevent entry of parasites, especially mites, into the tracheal system; and (3) they may reduce bulk flow of gases through the system caused by body movements, thereby reducing evaporative water loss. This would be disadvantageous in insects that ventilate the tracheal system, and it is of interest, therefore, that those spiracles important in ventilation commonly lack a sieve plate or have a plate that is divided down the middle so that it may be opened during ventilation.

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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