Asg

502 transport the fungi to new locations. Some ants and higher termites, for example, culture ascomycete or basidiomycete fungi in special regions of the nest called fungus gardens. Chewed wood or other vegetation is brought to the fungus garden and becomes the substrate on which the fungi grow, forming hyphae to be eaten by the insects. Certain wood-boring insects, for example, bark beetles (Scolytinae), inoculate their tunnels with fungal cells when they invade a new tree. The fungal mycelium that develops, along with partially decomposed wood, can then be used as food by the insects.

4.3. Absorption

The majority of absorption occurs in the midgut, especially the anterior portion, including the mesenteric ceca. A few reports have indicated that absorption of lipid materials (including the insecticides parathion and dieldrin) may occur across the crop wall, while the uptake of a range of small organic molecules occurs in the hindgut. The latter region is, however, primarily of importance as the site of water or ion resorption in connection with osmoregulation (Chapter 18, Section 4), though in insects that have symbiotic microorganisms in the hindgut it may also be an important site for absorption of small organic molecules, especially carboxylic and amino acids.

Most absorption of organic molecules across the midgut wall is passive, that is, from a higher to a lower concentration, though the rapid rate at which some molecules are absorbed suggests that special carriers facilitate their movement. The absorption rate is enhanced by a steep concentration gradient maintained between the midgut lumen and hemolymph. This may be achieved by absorption of water from the gut lumen so that the hemolymph becomes more dilute or by rapid conversion of the absorbed molecules to a more complex form. The absorption of organic molecules across the gut wall in Schistocerca and Periplaneta formed the subject of a series of papers by Treherne in the late 1950s (see Treherne, 1967, for details).

Using isotopically labeled monosaccharides, Treherne demonstrated that nearly all sugars are absorbed in the anterior region of the midgut, especially the ceca. Further, the monosaccharides are converted rapidly to the disaccharide trehalose in the fat body. Interestingly, in Schistocerca much of the fat body is in close proximity to the midgut wall. Of the monosaccharides studied, glucose was found to be absorbed most rapidly. Fructose and mannose are absorbed relatively slowly because of their accumulation in the hemolymph. The latter is related to the lower rate at which they are converted to trehalose. Apparently no mechanism for active uptake of monosaccharides occurs (or is necessary) in Schistocerca because its principal "blood sugar" is trehalose. In certain insects, for example, the honey bee, a considerable amount of glucose is normally present in the hemolymph and, in such species, active transport systems may be necessary for sugar absorption.

In Schistocerca, amino acids, like sugars, are apparently absorbed passively through the wall of the mesenteric ceca and anterior midgut. The observation that their absorption is passive is of interest, as it is known that the concentration of amino acids in the hemolymph is normally very high. Treherne discovered that, prior to amino acid absorption, there is rapid movement of water from the gut lumen to the hemolymph, which establishes a favorable concentration gradient for passive absorption of amino acids. In contrast, in lepidopteran larvae a suite of absorption mechanisms has been found (Turunen, 1985; Wolfersberger, 1996,2000; Sacchi and Wolfersberger, 1996). In high midgut concentrations the amino acids either diffuse passively across the gut wall or are moved on specific carriers (facilitated diffusion). At low concentrations, active uptake of amino acids occurs across the

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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