464 over the use of lipid substrates are its water solubility and the non-necessity of maintaining the metabolically expensive lipoprotein-carrier system.

Hormones regulate the supply of fuels to, and their use by, the flight muscles. Especially well studied is the control of flight metabolism in the migratory locust, Locusta migratoria, which uses carbohydrate for the first few minutes of flight but then converts to using mainly lipid. This early use of carbohydrate allows time for the hormonally controlled mobilization oflipid to gatherpace (Goldsworthy, 1983; Wheeler, 1989). When flight begins in the locust, hemolymph trehalose is the substrate oxidized, and its concentration steadily decreases for about 10 minutes. During this period, the release of adipokinetic hormones (AKH) from the corpora cardiaca begins. Three forms of AKH are known, of which two seem important in flight metabolism. AKH II, which is less abundant and has a short half-life, appears to be more important at the start of flight, activating fat body glycogen phosphorylase that converts glycogen to trehalose. Soon, however, AKH III, which is 14 times more common than AKH II and has a half-life >10 times that of AKH II, becomes dominant, promoting the mobilization of the stored lipid in the fat body. Specifically, the hormone activates triacylglycerol lipase that catalyzes the conversion of stored triglycerides into diglycerides, which are released into the hemolymph for use by the flight muscles (Gade and Auerswald, 1998; Van der Horst et al., 1999).

Because of their water-insoluble nature, the lipids are transported in the hemolymph bound to proteins (lipophorins) so that high concentrations can be achieved. The proteins are also important in receptor binding (recognizing the site for uptake of the lipids) and regulating lipid usage by the muscles (Haunerland, 1997). In addition, AKH induces a switch in metabolism of the flight muscles, stimulating them to preferentially use lipid rather than carbohydrate substrate. To this end, the muscles contain high concentrations of lipases and other enzymes required for hydrolysis of lipid and degradation of free fatty acids to two-carbon fragments that can be oxidized by the Krebs cycle to carbon dioxide and water.

AKH is also responsible for the mobilization of fat body carbohydrate, as well as the conversion of hemolymph alanine to proline, which also occurs in the fat body, in species that use these substrates in flight (Gade and Auerswald, 1998; Van der Horst et al., 1999; Goldsworthy and Joyce, 2001). Other hormones, including cardioaccelerating peptides, as well as the multifunctional molecule octopamine, are also released during flight, though their roles are not always clear (Elia et al., 1995; Candy et al., 1997). Orchard et al. (1993) have proposed two roles for octopamine in flight metabolism. First, the release of octopamine within the first few minutes of flight, coincident with a small, transient increase in hemolymph lipid, suggests that octopamine acts hormonally to trigger the initial release of lipid from the fat body. In vitro studies have confirmed that locust fat body releases lipid when octopamine is applied. Second, anatomical and physiological evidence indicates that the release of AKH is regulated by octopaminergic neurons that terminate in the glandular lobes of the corpora cardiaca, leading to the surge in hemolymph lipid seen after about 25 minutes.

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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