Structure

The innermost component of the integument (Figure 11.1) is the basal lamina, an amorphous but selectively porous acellular layer that is attached by hemidesmosomes to the epidermal cells. It is up to 0.5 thick and is produced mainly by the epidermis, though there are reports that hemocytes also participate. The chemical nature of the basal lamina is poorly understood though neutral mucopolysaccharide, glycoproteins, and collagen, similar to that of vertebrates, have been identified.

The epidermis (hypodermis) is a more or less continuous sheet of tissue, one cell thick, responsible for secreting the bulk of the cuticle. During periods of inactivity, its

unicellular dermal gland FIGURE 11.1. Diagrammatic cross-section of mature integument.

cells are flattened and intercellular boundaries are indistinct. When active, the cells are more or less cuboidal, and their plasma membranes are readily apparent; one to several nucleoli, extensive rough endoplasmic reticulum, and many Golgi complexes are evident (Locke, 1991, 1998). A characteristic feature of the apical (cuticle-facing) surface of epidermal cells are the plasma membrane plaques, specialized regions of the plasma membrane at the tips of fingerlike microvilli, from which the cuticulin envelope and new chitin fibers arise (Section 3.1). Electron microscopy has shown that, at metamorphosis, the epidermal cells develop basal processes ("feet") which can extend to become connected with the basal lamina and with other epidermal cells. When the feet shorten, the basal lamina is buckled and rearrangement of cells occurs, resulting in a change in the insect's shape, for example, from a long, thin caterpillar to a short, fat pupa (Locke, 1991, 1998). Epidermal cells also possess the ability to develop various forms of cytoskele-tal extensions which can be used, for example, to draw tracheoles closer to the cell for increased oxygen supply, or to maintain intercellular contact as the cells migrate during wound healing and changes in body shape. The density of cells in a particular area varies, following a sequence that can be correlated with the molting cycle. The cells often contain granules of a reddish-brown pigment, insectorubin, which in some insects contributes significantly to their color. However, in most insects color is produced by the cuticle (Section 4.3).

Epidermal cells may be differentiated into sense organs or specialized glandular cells. Oenocytes are large, ductless, often polyploid cells, up to 100 |am in diameter. They occur in pairs or small groups and the cells of each group may be derived from one original epidermal cell. Usually they move to the hemocoelic face of the basal lamina, though in some insects they form clusters in the hemocoel or migrate and reassemble within the fat body. Oenocytes show signs of secretory activity that can be correlated with the molting cycle, and, on the basis of certain staining reactions, it has been suggested that they produce the lipoprotein component of epicuticle. In addition, ultrastructural and biochemical studies have led to the proposal that these cells produce ecdysone (Locke, 1969; Romer, 1991). They also synthesize components of the cuticular wax, including some contact sex pheromones (Blomquist and Dillwith, 1985; Schal etal., 1998). Dermal glands of various types are also differentiated. In their simplest form the glands are unicellular and have a long duct that penetrates the cuticle to the exterior. More commonly, they are composed of several cells.

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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