Postembryonic Development

of the Scarabaeidae and other beetle families; campodeiform larvae occur in Neuroptera, 631

Coleoptera-Adephaga, and Trichoptera.

Polypod (eruciform) larvae (Figure 21.5C) have, in addition to thoracic legs, a varied number of abdominal prolegs. The larvae are generally phytophagous and relatively inactive, remaining close to or on their food source. The thorax and abdomen are weakly sclerotized in comparison with the head, which has well-developed chewing mouthparts. Eruciform larvae are typical of Lepidoptera, Mecoptera, and some Hymenoptera [sawflies (Tenthredinidae)].

Apodous larvae, which lack all trunk appendages, occur in various forms in many endopterygote orders but in common are adapted for mining in soil, mud, or animal or plant tissues. The variability of form concerns the extent to which a distinct head capsule is developed. In eucephalous larvae (Figure 21.5D), characteristic of some Coleoptera (Buprestidae and Cerambycidae), Strepsiptera, Siphonaptera, aculeate Hymenoptera, and more primitive Diptera (suborder Nematocera), the head is well sclerotized and bears normal appendages. The head and its appendages of hemicephalous larvae (Figure 21.5E) are reduced and partially retracted into the thorax. This condition is seen in crane fly larvae (Tipulidae: Nematocera) and in the larvae of orthorraphous Diptera. Larvae of Diptera-Muscomorpha are acephalous (Figure 21.5F); no sign of the head and its appendages can be seen apart from a pair of minute papillae (remnants of the antennae) and a pair of sclerotized hooks believed to be much modified maxillae.

Frequently a larva in the final instar ceases to feed and becomes inactive a few days before the larval-pupal molt. Such a stage is known as a prepupa. In some species, the entire instar is a non-feeding stage in which important changes related to pupation occur. For example, in the prepupal instar of sawflies, the salivary glands become modified for secreting the silk used in cocoon formation.

3.3.2. Heteromorphosis

In most endopterygotes the larval instars are more or less alike. However, in some species of Neuroptera, Coleoptera, Diptera, Hymenoptera, and in all Strepsiptera, a larva undergoes characteristic changes in habit and morphology as it grows, a phenomenon known as heteromorphosis (hypermetamorphosis). In such species several of the larval types described above may develop successively (Figure 21.6). For example, blister beetles (Meloidae) hatch as free-living campodeiform larvae (planidia, triungulins) that actively search for food (grasshopper eggs and immature stages, or food reserves of bees or ants). At this stage the larvae can survive for periods of several weeks without food. Larvae that locate food soon molt to the second stage, a caterpillarlike (eruciform) larva. The insect then passes through two or more additional larval instars, which may remain eruciform or become scarabaeiform. Some species overwinter in a modified larval form known as the pseudopupa or coarctate larva, so-called because the larva remains within the cuticle of the previous instar. The pseudopupal stage is followed the next spring by a further larval feeding stage, which then molts into a pupa.

3.3.3. The Pupal Stage

The pupa is a non-feeding, generally quiescent instar that serves as a mold in which adult features can be formed. For many species it is also the stage in which an insect survives adverse conditions by means of diapause (Chapter 22, Section 3.2.3). The terms "pupa" and "pupal stage" are commonly used to describe the entire preimaginal instar. This is,

FIGURE 21.6. Heteromorphosis in Epicauta (Coleoptera). (A) Triungulin; (B) caraboid second instar; (C) final form of second instar; (D) coarctate larva; (E) pupa; and (F) adult. [From J. W. Folsom, 1906, Entomology: With Special Reference to Its Biological and Economic Aspects, Blakiston.]

strictly speaking, incorrect because for a varied period prior to eclosion, the insect is a "pharate adult," that is, an adult enclosed within the pupal cuticle. The insect thus becomes an adult immediately after apolysis of the pupal cuticle and formation of the adult epicuticle (Chapter 11, Section 3.1). The distinction between the true pupal stage and the pharate adult condition becomes important in consideration of so-called "pupal movements," including locomotion and mandibular chewing movements (used in escaping from the protective cocoon or cell in which metamorphosis took place). In most instances these movements result from the activity of muscles attached to the adult apodemes that fit snugly around the remains of the pupal apodemes (Figure 21.7).

FIGURE 21.7. Section through mandible of a decticous pupa to show adult apodemes around remains of pupal apodemes. [After H. E. Hinton, 1946, A new classification of insect pupae, Proc. Zool. Soc. Lond. 116:282-328. By permission of the Zoological Society of London.]

FIGURE 21.8. Pupal types. (A) Decticous (Chrysopa sp., Neuroptera); (B) exarate adecticous (Brachyrhinus sulcatus, Coleoptera); and (C) obtect adecticous (Heliothis armigera, Lepidoptera). [From A. Peterson, 1951, Larvae of Insects. By permission of Mrs. Helen Peterson.]

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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