Summary

The removal of nitrogenous wastes and maintenance of a suitable hemolymph salt and water content are two closely linked processes. In most insects, the predominant nitrogenous waste is uric acid, which is removed from the hemolymph via the Malpighian tubules as the soluble sodium or potassium salt. Precipitation of uric acid occurs usually in the rectum as a result of resorption of ions and water from, and acidification of, the urine. Allantoin and allantoic acid are excreted in quantity by some insects and may be the major nitrogenous waste. Urea is of little significance as a waste product, and ammonia is generally produced only in aquatic species.

Insects are usually able to regulate the salt and water content of the hemolymph within narrow limits. In all insects, a primary excretory fluid, isosmotic with hemolymph but differing in ionic composition, is produced in the Malpighian tubules. Production of tubule fluid is driven by active transport of potassium ions. When this fluid reaches the posterior rectum, it is modified according to an insect's needs. In terrestrial insects selective resorption of ions and/or water occurs. Freshwater species osmoregulate by producing hy-poosmotic urine from which useful materials have been resorbed. In a hyperosmotic medium they become osmoconformers, their hemolymph osmotic pressure paralleling that of the medium. Brackish-water and saltwater insects have excellent ability to osmoregulate over a wide range of environmental conditions. In dilute media they behave much like freshwater species, forming hypoosmotic urine and resorbing useful components. In media with osmotic pressures greater than that of hemolymph, saltwater species drink excessively and produce hyperosmotic urine by secreting ions across the rectal wall; in contrast, brackish-water insects osmoconform by increasing the concentration of amino acids and trehalose in the hemolymph.

Both diuretic and antidiuretic hormones are known. The former stimulate Malpighian tubule fluid production and may inhibit water resorption from the rectum; antidiuretic hormones mostly appear to act only by stimulating water resorption from the rectal lumen; however, in a few species the antidiuretic factor inhibits potassium ion transport (hence formation of the primary excretory fluid) in the Malpighian tubule.

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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