Holometabolous Development

Holometabolous development, in which there is a marked change of form from larva to adult (complete metamorphosis), occurs in endopterygotes and a few exopterygotes, for example, whiteflies (Aleurodidae: Hemiptera), thrips (Thysanoptera), and male scale insects (Coccidae: Hemiptera). Perhaps the most obvious structural difference between the larval and adult stages of endopterygotes is the absence of any external sign of wing development in the larval stages. The wing rudiments develop internally from imaginal discs that in most larvae lie at the base of the peripodial cavity, an invagination of the epidermis beneath the larval cuticle, and are evaginated at the larval-pupal molt (see Section 4.2 and Figure 21.11).

As noted above, the evolution of a pupal stage in the life history has made holometabolous development possible. The pupa is probably a highly modified final juvenile instar (Chapter 2, Section 3.3) which, through evolution, became less concerned with feeding and building up reserves (this function being left to earlier instars) and more

FIGURE 21.4. Basic types of development in insects. Broken arrow indicates several molts.

Ametabolous

Hemimetabolous Holometabolous

FIGURE 21.4. Basic types of development in insects. Broken arrow indicates several molts.

630 specialized for the breakdown of larval structures and construction of adult features. In other words, the pupa has become a non-feeding stage; it is generally immobile as a result of histolysis of larval muscles; it broadly resembles the adult and thereby serves as a mold for the formation of adult tissues, especially muscles.

3.3.1. The Larval Stage

Among endopterygotes the extent to which the larval and adult habits and structure differ [and therefore the extent of metamorphosis (Section 4.2)] is varied. Broadly speaking, in members of more primitive orders the extent of these differences is small, whereas the opposite is true, for example, in the Hymenoptera and Diptera. Endopterygote larvae can be arranged in a number of basic types (Figure 21.5). The most primitive larval form is the oligopod. Larvae of this type have three pairs of thoracic legs and a well-developed head with chewing mouthparts and simple eyes. Oligopod larvae can be further subdivided into (1) scarabaeiform larvae (Figure 21.5A), which are round-bodied and have short legs and a weakly sclerotized thorax and abdomen, features associated with the habit of burrowing into the substrate, and (2) campodeiform larvae (Figure 21.5B), which are active, predaceous surface-dwellers with a dorsoventrally flattened body, long legs, strongly scle-rotized thorax and abdomen, and prognathous mouthparts. Scarabaeiform larvae are typical

FIGURE 21.5. Larval types. (A) Scarabaeiform (Popillia japonica, Coleoptera); (B) campodeiform (Hippo-damia convergens, Coleoptera); (C) eruciform (Danaus plexippus, Lepidoptera); (D) eucephalous (Bibio sp., Diptera); (E) hemicephalous (Tanyptera frontalis, Diptera); and (F) acephalous (Musca domestica, Diptera). [A-E, from A. Peterson, 1951, Larvae of Insects. By permission of Mrs. Helen Peterson. F, from V. B. Wigglesworth, 1959, Metamorphosis, polymorphism, differentiation, Scientific American, February 1959. By permission of Mr. Eric Mose, Jr.]

FIGURE 21.5. Larval types. (A) Scarabaeiform (Popillia japonica, Coleoptera); (B) campodeiform (Hippo-damia convergens, Coleoptera); (C) eruciform (Danaus plexippus, Lepidoptera); (D) eucephalous (Bibio sp., Diptera); (E) hemicephalous (Tanyptera frontalis, Diptera); and (F) acephalous (Musca domestica, Diptera). [A-E, from A. Peterson, 1951, Larvae of Insects. By permission of Mrs. Helen Peterson. F, from V. B. Wigglesworth, 1959, Metamorphosis, polymorphism, differentiation, Scientific American, February 1959. By permission of Mr. Eric Mose, Jr.]

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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