Abdominal Appendages

Generally the only appendages seen on the abdomen of an adult pterygote insect are those on the genital segments (the external genitalia) and the cerci. In the apterygote groups i \ i \ jS FIGURE 3.30. Postgenital segments of a female grasshop-

\ .V^oviíiíitoi- per. [From R. E. Snodgrass, Principles of Insect Morphology. Y"-\ Copyright 1935 by McGraw-Hill, Inc. Used with permission of

Male Pregenital Segments

there are, in addition, appendages on a varied number of pregenital segments. All of these 85

may be considered as "primary" appendages, that is, derived from the primitive insect limb.

Many larvae possess segmentally arranged prolegs or gills on the abdomen. Accord- structure ing to some authorities (e.g., Hinton, 1955), these are secondary structures and are not derived from the primitive limb. However, others, notably Kukalova-Peck (1991), have argued that these are homologues of the thoracic legs, that is, are direct descendants of the ancestral paired appendages present on all segments. Finally, a number of insects possess non-segmental appendages on the abdomen, which clearly are of secondary origin.

5.2.1. External Genitalia

The morphology of the external genitalia is highly varied, especially in the male, and it is sometimes extremely difficult to homologize the different components. In the female the appendages combine to form an ovipositor, used for placing eggs in specific sites. The appendages of the male are used as clasping organs during copulation. Because of their specific form, the external genitalia are widely used by taxonomists for identification purposes.

Female. According to Scudder (1961) the primitive structure of the pterygote insect ovipositor can be seen in the silverfish Lepisma (Figure 3.31A). The ovipositor typically has a basal part and a shaft. The basal part consists of two pairs of gonocoxae (valvifers) on the eighth and ninth segments, homologous with the coxa of the leg. Projecting ventroposteriorly from each gonocoxa is an elongate process, the gonapophysis (valvula). Together the four gonapophyses make up the shaft. The first gonapophyses are ventral, the second dorsal. In most pterygote orders the second gonocoxa has a second posterior process, the third valvula or gonoplac, attached to it (Figure 3.31B). The gonoplac may form part of the ovipositor or serve as a protective sheath. The gonangulum is a small sclerite, articulated with the second gonocoxa (from which it is derived) and the ninth tergum.

Among Pterygota an ovipositor is found in Grylloblattodea, Dictyoptera, Orthoptera, and Hymenoptera, some Odonata and most Hemiptera, Thysanoptera, and Psocoptera. In each of these groups it is more or less modified from the general condition described above. The ovipositor of Odonata and Grylloblattodea is almost identical with that of Lepisma, except that a gonoplac is present. In Dictyoptera and Orthoptera the gonangulum fuses with the first gonocoxa. In viviparous cockroaches the ovipositor is considerably modified. The gonoplac, in Orthoptera, is a large sclerotized plate that forms part of the ovipositor shaft. The second gonapophyses, when present, are usually median and concealed. These structures are much reduced in Acrididae.

In Hemiptera, Thysanoptera, and Psocoptera, an ovipositor may or may not be present. When present, the gonangulum is fused with the ninth tergum, and the second gonapophyses are fused, making the shaft a three-part structure. The gonoplacs normally ensheath the shaft.

The ovipositor of Hymenoptera may be considerably modified for boring, piercing, sawing, and stinging (Figure 3.32). Only when modified for stinging does it no longer participate in egg laying, though it retains the basic components, with the exception of the first gonocoxae, which have disappeared. The first gonapophyses are attached to the gonangu-lum, which is articulated with the ninth tergum and second gonocoxa. As in Hemiptera, the second gonapophyses are fused. The shaft is typically very elongate, and the eggs are considerably compressed as they are squeezed along it. In the stinging Hymenoptera the eggs are released at the base of the ovipositor. The fused second valvulae form an inverted

Zygentoma Ovipositor

FIGURE 3.31. Structure of the ovipositor. (A) Lepisma (Zygentoma); and (B) a typical pterygote insect. [A, after G. G. E. Scudder, 1961, The comparative morphology of the insect ovipositor, Trans. R. Entomol. Soc. Lond. 113:25-40. By permission of the Royal Entomological Society. B, from R. E. Snodgrass, Principles of Insect Morphology. Copyright 1935 by McGraw-Hill, Inc. Used with permission of McGraw-Hill Book Company.]

FIGURE 3.31. Structure of the ovipositor. (A) Lepisma (Zygentoma); and (B) a typical pterygote insect. [A, after G. G. E. Scudder, 1961, The comparative morphology of the insect ovipositor, Trans. R. Entomol. Soc. Lond. 113:25-40. By permission of the Royal Entomological Society. B, from R. E. Snodgrass, Principles of Insect Morphology. Copyright 1935 by McGraw-Hill, Inc. Used with permission of McGraw-Hill Book Company.]

Bee Stinger Anatomy
FIGURE 3.32. Sting of the honey bee. [After R. E. Snodgrass, 1925. Anatomy and Physiology of the Honey bee. McGraw-Hill Book Company.]

ejaculatory I duct

phallotreme aedeagus c

FIGURE 3.33. Origin and development of the phallic organs. (A) Primary phallic lobes; (B) paired penes of Ephemeroptera; and (C) formation of the aedeagus. [Reproduced by permission of the Smithsonian Institution Press from Smithsonian Miscellaneous Collections, Volume 135, "A revised interpretation of the external reproductive organs of male insects," Number 6, December 3, 1957, 60 pages, by R. E. Snodgrass: Figures 1A-C, page 3. Washington, D.C., 1958, Smithsonian Institution.]

ejaculatory I duct

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Beekeeping for Beginners

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