Carbohydrate Metabolism

As in other animals, simple sugars provide a readily available substrate that can be oxidized for production of energy. However, in contrast to vertebrates where glucose in the blood is the sugar of importance as an energy source, in insect hemolymph glucose and other monosaccharides usually are present only in minimal amounts. An exception to this statement is the worker honey bee whose hemolymph glucose may reach a concentration of almost 3 g/100 ml and is used as the energy source during flight. In most insects, a disaccharide, trehalose, is the immediate energy source. Trehalose consists of two glucose molecules joined through an a1, 1-linkage. Its level in the hemolymph is constant and in a state of dynamic equilibrium with glycogen stored in the fat body (Friedman, 1978). In this respect, therefore, the situation is comparable to that in vertebrates whose blood glucose level is in equilibrium with liver glycogen. The similarity goes further. Just as the conversion of liver glycogen to blood glucose is promoted by the hormone glucagon, which stimulates glycogen phosphorylase activity, in insect fat body the formation of trehalose from glycogen is promoted by a hyperglycemic hormone released from the corpora cardiaca. This hormone activates the phosphorylase, which removes a glucose unit from the glycogen. Because of its highly polar, polyhydroxyl nature, trehalose does not easily penetrate the muscle cell membrane. Therefore, before it can be oxidized by muscle it must first be converted into glucose by a hydrolyzing enzyme, trehalase, present in the muscle cell membrane. Hemolymph trehalose is also the source of the glucose that is converted by epidermal cells into acetylglucosamine during production of the nitrogenous polysaccharide chitin (Chapter 11, Section 3.1).

Glycogen is an important reserve substance in almost all insects and is found in high concentration in the fat body, with smaller amounts in muscle, especially flight muscle, and sometimes the midgut epithelium. In the mature bee larva, for example, glycogen makes up about one-third of the dry weight. It is produced principally from glucose and other monosaccharides absorbed from the gut following digestion. In some insects glycogen may also be synthesized from amino acids. As noted above, fat body glycogen (and perhaps also that stored in the midgut epithelium) is used to maintain a constant level of trehalose

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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