Embryonic Development

FIGURE 20.13. Early development of Litomastix (Hymenoptera). (A) Fertilization; (B) first cleavage; (C) two-cell stage; (D-F) next stages; (G) formation of spindle cells; and (H) formation of secondary embryonic masses. [After O. M. Ivanova-Kasas, 1972, Polyembryony in insects, in: Developmental Systems: Insects, Vol. I (S. J. Counce and C. H. Waddington, eds.). By permission of Academic Press Ltd., and the author.]

the larva that emerges from a newly laid egg molts immediately to the second instar; in Termitoxenia, whose egg is relatively larger, it is a third-instar larva that emerges from an egg and it pupates within a few minutes.

In truly viviparous species, developing offspring obtain their food from the mother. Accordingly, the structures of the maternal reproductive system and egg are modified to facilitate this exchange. As in ovoviviparity, the trend is toward reduction of the number of embryos being developed simultaneously.

Some aphids, Psocoptera, and Dermaptera (Hemimerus) show pseudoplacental viviparity (Hagan, 1951). Eggs of these insects contain little or no yolk and lack a chorion. They develop within the ovariole, where the follicle cells supposedly supply at least some nourishment to the embryo. (In species with meroistic ovarioles, the nurse cells are also important). In Hemimerus, for example, follicle cells adjacent to the anterior and posterior ends of an oocyte proliferate and become connected with the embryonic membranes forming pseu-doplacentae. Later, the follicle cells degenerate because, it is assumed, they are supplying nutrients to the developing embryo (Figure 20.16).

FIGURE 20.14. Caterpillars parasitized by Litomastix. [From R. R. Askew, 1971, Parasitic Insects. By permission of Heinemann Educational Books Ltd.]

FIGURE 20.14. Caterpillars parasitized by Litomastix. [From R. R. Askew, 1971, Parasitic Insects. By permission of Heinemann Educational Books Ltd.]

FIGURE 20.15. Female reproductive system of the tachinid Panzeria (Díptera). (A) Newly emerged fly; and (B) mature female, with greatly enlarged vagina forming a brood chamber. An egg containing a fully formed embryo is being laid, [After V. B. Wigglesworth, 1965, The Principles of Insect Physiology, 6th ed., Methuen and Co. By permission of the author.]

FIGURE 20.15. Female reproductive system of the tachinid Panzeria (Díptera). (A) Newly emerged fly; and (B) mature female, with greatly enlarged vagina forming a brood chamber. An egg containing a fully formed embryo is being laid, [After V. B. Wigglesworth, 1965, The Principles of Insect Physiology, 6th ed., Methuen and Co. By permission of the author.]

In Glossina spp. and pupiparous Diptera adenotrophic viviparity occurs. In this arrangement, an egg is normal, that is, contains yolk and possesses a chorion, yet is retained within the expanded bursa, the so-called uterus. Embryonic development is, therefore, correctly described as ovoviviparous. However, after hatching, the larva remains within the uterus and feeds on secretions (uterine milk) of the enormous accessory glands that ramify through the abdomen (Figure 20.17). One larva at a time develops and pupation occurs shortly afterbirth.

In hemocoelic viviparity, used by Strepsiptera and some paedogenetic Cecidomyiidae (Diptera), oocytes are released from the ovarioles into the maternal hemocoel. In Strepsiptera fertilization occurs within the maternal body cavity, and, during embryonic development,

FIGURE 20.16. Longitudinal section through ovarian follicle of Hemimerus (Dermaptera) to show pseudoplacentae. (After V. B. Wigglesworth, 1965, The Principles of Insect Physiology, 6th ed., Methuen and Co. By permission of the author.]

duct of spermatheca accessory (uterine) glands

FIGURE 20.17. Female reproductive system of Glossina (Diptera) to show enlarged accessory glands. Note also that only one egg at a time is maturing. [After V. B. Wigglesworth, 1965. The Principles of Insect Physiology, 6th ed., Methuen and Co. By permission of the author.]

duct of spermatheca accessory (uterine) glands

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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