Freshwater Insects

In freshwater insects water enters the body osmotically despite the relatively impermeable cuticle (Chapter 11, Section 4.2) and must be removed, and salts will be lost from the body and must be replaced if the hyperosmotic condition of the hemolymph is to be maintained. Freshwater insects can regulate their hemolymph osmotic pressure successfully to the point at which the external environment becomes isosmotic with the hemolymph (Figure 18.6). This is achieved by the production of urine that is hypoosmotic to the hemolymph. Beyond this point, regulation breaks down because freshwater insects are not able to produce hyperosmotic urine; that is, they cannot resorb water against a concentration gradient or excrete excess ions (Stobbart and Shaw, 1974). In other words, they become osmoconformers, their hemolymph osmotic pressure closely paralleling that of the external medium.

As in terrestrial insects, the Malpighian tubules produce a fluid that is isosmotic with the hemolymph but of different ionic composition. Particularly obvious is the great difference in the potassium ion concentration between the two solutions, as a result of active transport (Table 18.2). When the primary urine enters the rectum, resorption of ions occurs. The osmotic pressure of the fluid that finally leaves the body is much lower than that of the hemolymph but not as low as would be expected from knowledge of the extent of ion resorption in the rectum. This is because large quantities of ammonium ions appear in the rectal fluid. These ions cannot be detected in the Malpighian tubules, and it is presumed that they are secreted directly across the rectal wall, as occurs in larvae of S. bullata (Section 2.2).

Osmotic pressure of medium as % NaCI

FIGURE 18.6. The relationship between osmotic pressure of the hemolymph and that of the external medium in some freshwater insects. [After J. Shaw and R. H. Stobbart, 1963, Osmotic and ionic regulation in insects, Adv. Insect Physiol. 1:315-399. By permission of Academic Press Ltd. and the authors.]

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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