Reproduction

FIGURE 19.5. (A) Section through testis to show arrangement of follicles; and (B) zones of maturation in testis follicle. [A, from R. E. Snodgrass, Principles of Insect Morphology. Copyright 1935 by McGraw-Hill, Inc. Used with permission of McGraw-Hill Book Company. B, after V. B. Wigglesworth, 1965, The Principles of Insect Physiology, 6th ed., Methuen and Co. By permission of the author.]

Dictyoptera, Hemiptera, and Lepidoptera a prominent apical cell is also present whose presumed function is to supply nutrients to the spermatogonia. As each spermatogonium moves proximally into the zone of growth, it becomes enclosed within a layer of somatic cells, forming a "cyst." Within the cyst, the cell divides mitotically to form a varied number (usually 64-256) of spermatocytes. In the zone of maturation, the spermatocytes undergo two maturation divisions, so that from each spermatocyte four haploid spermatids are formed. In the proximal part of the follicle, the zone of transformation, spermatids differentiate into flagellated spermatozoa. At this time the cyst wall normally has ruptured, though often the sperm within a bundle (spermatodesm) remain held together by a gelatinous cap that covers their anterior end. This cap may be lost as the sperm enter the vas deferens or persist until the sperm have been transferred to the female.

In Lepidoptera two types of sperm occur. Pyrene (nucleate) sperm are those that fertilize eggs, while apyrene (anucleate) sperm are speculated to have several functions, including assisting in the movement of pyrene sperm from the testes to the seminal vesicles, providing nourishment to the pyrene sperm, and destroying sperm from previous matings (Silberglied et al., 1984). In each species within the Drosophila obscura complex two size classes of

568 nucleated sperm are produced, which differ in head and tail lengths. Snook and Karr (1998)

confirmed that only the long-sperm type fertilize eggs, though the function(s) of the short

sperm remain unidentified.

Sperm are moved from the testes to their site of storage (normally, the seminal vesicles) by peristaltic contractions of the vas deferens. The seminal vesicles are dilations of the vasa deferentia. Their walls are well tracheated and frequently glandular, which may indicate a possible nutritive function. In Acrididae (Orthoptera) sperm are stored in a pair of highly modified accessory gland tubules (Figure 19.4A). In many Lepidoptera the migration of sperm follows a circadian rhythm (Giebultowicz et al, 1989). Typically sperm are released from the testes into the upper vasa deferentia shortly before or just after dark, and then are moved into the seminal vesicles during the next light phase. However, they quickly leave this site, being moved into the duplex region of the reproductive tract (Figure 19.4C), where they remain until the next copulation occurs. The timing of sperm movement is such that the sperm produced each day move into the duplex a few hours after the male's daily period of receptivity to female pheromone. This ensures that when the male next has an opportunity to mate, a substantial amount of new sperm will be available for insemination.

The vasa deferentia enter the anterior tip of the ejaculatory duct, an ectodermally derived tube lined with cuticle whose walls normally are heavily muscularized. Posteriorly, the ejaculatory duct may run through an evagination of the body wall, which thus forms an intromittent organ. In insects that form a complex spermatophore, subdivision of the ejaculatory duct into specialized regions may occur. In Ephemeroptera no ejaculatory duct is present, and each vas deferens opens directly to the exterior.

The accessory glands may be either mesodermal (mesadenia) or ectodermal (ectadenia) in origin and are connected with either the lower part of the vasa deferentia or the upper end of the ejaculatory duct. In some species considerable morphological and functional differentiation of the glands occurs. Essentially, however, their secretions may contribute to the seminal fluid and/or form the spermatophore. In some species the glands produce substances that, when transferred to the female during insemination, cause increased egg production (Section 3.1.3) and/or decreased receptivity (willingness to mate subsequently) (Gillott, 1988, 2003).

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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