Other Excretory Structures

Even in insects that use the rectum as the primary site of osmoregulation, the ileum may nonetheless be a site for water or ion resorption. In other species where the rectum is unimportant in osmoregulation, serving only to store urine and feces prior to expulsion, the ileum often takes on this role.

In a few insects the labial glands may function as excretory organs. In apterygotes that lack Malpighian tubules the glands can accumulate and eliminate dyes such as ammonia carmine and indigo carmine from the hemolymph, but there is no evidence that they can deal similarly with nitrogenous or other wastes. The labial glands of saturniid moths excrete copious amounts of fluid just prior to emergence from the cocoon, and it may well be that the primary function of the glands is to reduce hemolymph volume and hence body weight, which, in such large flying insects, needs to be kept as low as possible. The midgut of silkmoth larvae actively removes potassium from the hemolymph, thus protecting the tissues from the very high concentration of potassium ions present in the leaves eaten by these insects.

In a few insects it appears that the Malpighian tubules, though present, play no part in nitrogenous excretion. In Periplaneta americana, for example, uric acid is not found in the tubules but does occur in small amounts in the hindgut, which may excrete it directly from the hemolymph. In P. americana much uric acid is stored in urate cells in the fat body, and the major form of excreted nitrogen in this species is ammonia. How this reaches the hindgut lumen in P. americana is unclear. However, in the flesh fly Sarcophaga bullata, ammonia, the primary excretory product, is actively secreted as ammonium ions into the lumen across the anterior hindgut wall.

FIGURE 18.2. Cryptonephridial arrangement of Malpighian tubules in Tenebrio larva. (A) General appearance. Note that only three of the six tubules are drawn fully and that in reality the tubules are much more convoluted and have more boursouflures than are shown; (B) cross section through posterior region of cryptonephridial system; (C) details of a leptophragma; and (D) diagram illustrating proposed mode of operation of system. Solid arrows indicate movements of potassium, hollow arrows indicate movements of water. Numbers indicate osmotic concentration (measured as freezing-point depression) of fluids in different compartments. [After A. V. Grimstone, A. M. Mullinger, and J. A. Ramsay, 1968, Further studies on the rectal complex of the mealworm Tenebrio molitor L. (Coleoptera, Tenebrionidae), Philos. Trans. R. Soc. Lond. Ser. B 253:343-382. By permission of the Royal Society, London, and Professor J. A. Ramsay.]

FIGURE 18.2. Cryptonephridial arrangement of Malpighian tubules in Tenebrio larva. (A) General appearance. Note that only three of the six tubules are drawn fully and that in reality the tubules are much more convoluted and have more boursouflures than are shown; (B) cross section through posterior region of cryptonephridial system; (C) details of a leptophragma; and (D) diagram illustrating proposed mode of operation of system. Solid arrows indicate movements of potassium, hollow arrows indicate movements of water. Numbers indicate osmotic concentration (measured as freezing-point depression) of fluids in different compartments. [After A. V. Grimstone, A. M. Mullinger, and J. A. Ramsay, 1968, Further studies on the rectal complex of the mealworm Tenebrio molitor L. (Coleoptera, Tenebrionidae), Philos. Trans. R. Soc. Lond. Ser. B 253:343-382. By permission of the Royal Society, London, and Professor J. A. Ramsay.]

In males of some species of cockroaches, for example, Blattella germanica, a considerable amount of uric acid (as much as 5% of the live weight of the insect) is found in the utriculi majores (part of the accessory reproductive gland complex). The uric acid becomes part of the wall of the spermatophore and is, in a sense, "excreted" during copulation.

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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