Chapter

564 consists of a terminal filament, germarium, vitellarium, and pedicel (ovariole stalk). The terminal filaments may fuse to form a sheet of tissue attached to the dorsal body wall or dorsal diaphragm by which an ovary is suspended within the abdominal cavity. Within the germarium, oogonia, derived from primary germ cells, give rise to oocytes and, in some types of ovarioles, also to nutritive cells (see below). As oocytes mature and enter the vitellarium they tend in most insects to become arranged in a linear sequence along the ovariole. Each oocyte also becomes enclosed in a one-cell-thick layer of follicular epithelium derived from mesodermal prefollicular tissue located at the junction of the germarium and vitellarium. As its name indicates, the vitellarium is the region in which an oocyte accumulates yolk, a process known as vitellogenesis (Section 3.1.1). Normally vitellogenesis occurs only in the terminal oocyte, that is, the oocyte closest to the lateral oviduct, and during the process the oocyte's volume may increase enormously, for example, by as much as 105 times in Drosophila. Each ovariole is connected to a lateral oviduct by a thin-walled tube, the pedicel, whose lumen is initially occluded by epithelial tissue. This plug of tissue is lost during ovulation (movement of a mature oocyte into a lateral oviduct) and replaced by the remains of the follicular epithelium that originally covered the oocyte. Ovarioles may join a lateral oviduct linearly, as in some apterygotes, Ephemeroptera and Orthoptera, or, more often, open confluently into the distal expanded portion of the oviduct, the calyx.

Three types of ovarioles can be distinguished (Figure 19.2). The most primitive type, found in Thysanura, Paleoptera, most orthopteroid insects, Siphonaptera, and some Mecoptera, is the panoistic ovariole in which specialized nutritive cells (trophocytes) are absent. Trophocytes occur in the two remaining types, the polytrophic and telotrophic ovarioles, which are sometimes grouped together as meroistic ovarioles. In polytrophic ovarioles, several trophocytes (nurse cells) are enclosed in each follicle along with an oocyte. The trophocytes and oocyte originate from the same oogonium. Polytrophic ovarioles are found in most endopterygotes, and in Dermaptera, Psocoptera, and Phthiraptera. In Hemiptera and Coleoptera telotrophic (acrotrophic) ovarioles occur in which the trophocytes form a syncytium in the proximal part of the germarium and connect with each oocyte by means of a trophic cord.

The lateral oviducts are thin-walled tubes that consist of an inner epithelial layer set on a basal lamina and an outer sheath of muscle. In many species they include both mesodermal and ectodermal components. In almost all insects they join the common oviduct medially beneath the gut, but in Ephemeroptera the lateral oviducts remain separate and open to the exterior independently. The common oviduct, which is lined with cuticle, is usually more muscular than the lateral oviducts. Posteriorly, the common oviduct is confluent with the vagina that, as noted above, may evaginate to form the bursa copulatrix. In some species the bursa forms a diverticulum off the oviduct. In nearly all Lepidoptera the bursa is physically distinct from the oviduct and opens to the outside viathe vulva (Figure 19.3). A narrow sperm duct connects the bursa with the oviduct and forms the route along which the sperm migrate to the spermatheca.

Usually a single spermatheca is present in which sperm are stored, though in some higher Diptera up to three such structures occur. The spermatheca and the duct with which it joins the bursa are lined with cuticle. The cuticle overlays a one-cell-thick layer of epithelium whose cells are glandular and assumed to secrete nutrients for use by the stored sperm. Typically, also, the cells have a much folded apical plasmalemma, adjacent to which are many mitochondria, features characteristic of cells involved in ion exchange (compare the structure of Malpighian tubule and rectal epithelial cells, Chapter 18, Sections 2.1

FIGURE 19.3. Reproductive system of female Lepidoptera-Ditrysia. [After A. D. Imms, 1957, A General Textbook of Entomology, 9th ed. (revised by O. W. Richards and R. G. Davies), Methuen and Co.]

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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