Brackish Water and Saltwater Insects

Brackish water may be defined as water whose osmotic concentration is in the range 300 mOsm (about 1.1% sodium chloride) (the osmotic concentration of the hemolymph) to 1000 mOsm (about 3.5% sodium chloride) (the concentration of normal seawater), with salt water having osmotic concentrations greater than those of natural seawater. The definitions

FIGURE 18.7. (A) Posterior end of Aedes aegypti to show anal papillae; and (B) structural details of a single anal papilla. [A, after V. B. Wigglesworth, 1965, The Principles of Insect Physiology, 6th ed., Methuenand Co. By permission of the author. B, after V. B. Wigglesworth, 1933, The effect of salts on the anal glands of the mosquito larva, J. Exp. Biol. 10:1-15. By permission of Cambridge University Press.]

FIGURE 18.7. (A) Posterior end of Aedes aegypti to show anal papillae; and (B) structural details of a single anal papilla. [A, after V. B. Wigglesworth, 1965, The Principles of Insect Physiology, 6th ed., Methuenand Co. By permission of the author. B, after V. B. Wigglesworth, 1933, The effect of salts on the anal glands of the mosquito larva, J. Exp. Biol. 10:1-15. By permission of Cambridge University Press.]

are not entirely arbitrary, as they tend to describe habitats occupied by particular species. For example, larvae of the mosquito Culiseta inornata are found in a variety of brackish waters, including tidal estuaries and some inland ponds, but cannot survive in natural seawater. In contrast, larvae of Aedes taeniorhynchus, which occur in coastal salt marshes, have a maximum saline tolerance equivalent to 10% sodium chloride. Even more remarkable are larvae of Ephydra cinerea that are found in the Great Salt Lake of Utah where the salinity may exceed the equivalent of 20% sodium chloride (i.e., about six times that of normal seawater).

The habitat occupied by brackish-water and saltwater insects can vary widely in ionic content and osmotic pressure. During periods of warm, dry weather the salinity may increase several fold. Conversely, after heavy rains or the melting of snow in spring, the salinity may approach that of fresh water. It is not surprising, therefore, to find experimentally that such insects can regulate their hemolymph osmotic pressure over a wide range of external salt concentrations (Figure 18.8). Larvae of Aedes detritus and Ephydra riparia, inhabitants of salt marshes, can survive in media containing the equivalent of 0 to about 7-8% sodium chloride. Over this range of concentrations the hemolymph osmotic pressure changes by only 40-60%.

When their external medium is dilute (i.e., its osmotic pressure is less than that of the hemolymph), both brackish-water and saltwater insects osmoregulate to keep their

FIGURE 18.8. The relationship between osmotic pressure of the hemolymph and that of the external medium in some saltwater (sw) and brackish-water (bw) larvae. [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.]

FIGURE 18.8. The relationship between osmotic pressure of the hemolymph and that of the external medium in some saltwater (sw) and brackish-water (bw) larvae. [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.

Get My Free Ebook


Post a comment