Postembryonic Development

FIGURE 21.9. Imaginal discs of Drosophila and their derivatives in the adult body. [From H. Wildermuth, 1970, Determination and transdetermination in cells of the fruitfly, Sci. Prog. (Oxford) 58:329-358. By permission of Blackwell Scientific Publications.]

are groups of loosely associated cells in the larval integument, do secrete larval cuticle. At metamorphosis, under hormonal influence, they divide and differentiate into the adult abdominal epidermis, fat body, oenocytes, and some muscles.

With the evolution of imaginal discs the way was open for the development of a larva whose form is highly different from that of the adult, and capable of existing in a different habitat from that of the adult, thus avoiding competition for food and space.

To clarify the histological changes that occur in endopterygote metamorphosis, the various organ systems will be considered separately

Epidermal cells carried over from the larval stage produce the cuticle of most adult endopterygotes. However, in Hymenoptera-Apocrita and Diptera-Muscomorpha the larval epidermis is more or less completely histolyzed and replaced by cells derived from imaginal discs and histoblasts. In Muscomorpha, histolysis of the larval epidermis does not occur until after pupariation.

Appendage formation is also varied. In lower endopterygotes formation of adult mouth-parts, antennae, and legs begins early in the final larval stadium from larval epidermis. Certain predetermined areas of the epidermis thicken, then proliferate and differentiate so that, at pupation, the basic form of the adult appendages is evident. During the pupal stadium the final form of the adult appendages is expressed (Figure 21.10). In contrast, where the larval appendages are very different from those of the adult, or are absent, the adult structures develop from imaginal discs that undergo marked proliferation and differentiation in the last larval instar and are evaginated from the peripodial cavity at the larval-pupal molt. Wings are formed in all endopterygotes from imaginal discs. In most species their early development is similar to the development of paired segmental appendages outlined above; that is, the wing rudiments form in a peripodial cavity and become everted at the larval-pupal molt (Figure 21.11). The forming wing bud in the peripodial cavity is initially a hollow,

FIGURE 21.10. Sections through leg of Pieris (Lepidoptera) to show development of adult appendage. (A) Leg of last-instar larva 3 hours after ecdysis; (B) same as (A) but 1 day after ecdysis; (C) same as (A) but 3 days after ecdysis; (D) leg at beginning of prepupal stage showing presumptive areas of adult leg; and (E) leg of pupa. [After C.-W. Kim, 1959, The differentiation center inducing the development from larval to adult leg in Pieris brassicae (Lepidoptera), J. Embryol. Exp. Morphol. 7:572-582. By permission of Cambridge University Press.]

FIGURE 21.10. Sections through leg of Pieris (Lepidoptera) to show development of adult appendage. (A) Leg of last-instar larva 3 hours after ecdysis; (B) same as (A) but 1 day after ecdysis; (C) same as (A) but 3 days after ecdysis; (D) leg at beginning of prepupal stage showing presumptive areas of adult leg; and (E) leg of pupa. [After C.-W. Kim, 1959, The differentiation center inducing the development from larval to adult leg in Pieris brassicae (Lepidoptera), J. Embryol. Exp. Morphol. 7:572-582. By permission of Cambridge University Press.]

FIGURE 21.11. Sections through developing wing bud of first four larval instars of Pieris (Lepidoptera). [After J. H. Comstock, 1918, The Wings of Insects, Comstock.]

FIGURE 21.12. Transverse sections of developing wing of Drosophila. (A, B) Successive stages in pharate pupa; (C-G) stages in pupa; and (H) pharate adult. [After C. H. Waddington, 1941, The genetic control of wing development in Drosophila, J. Genet. 41:75-139. By permission of Cambridge University Press.]

FIGURE 21.12. Transverse sections of developing wing of Drosophila. (A, B) Successive stages in pharate pupa; (C-G) stages in pupa; and (H) pharate adult. [After C. H. Waddington, 1941, The genetic control of wing development in Drosophila, J. Genet. 41:75-139. By permission of Cambridge University Press.]

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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