FIGURE 3.35. Secondary segmental appendages. (A) Proleg of a caterpillar; and (B) gill of a mayfly larva. [From R. E. Snodgrass, Principles of Insect Morphology. Copyright 1935 by McGraw-Hill, Inc. Used with permission of McGraw-Hill Book Company.]

Prolegs. Segmentally arranged, leglike structures are present on the abdomen of many endopterygote larvae (Figure 3.35A). They are known as prolegs (pseudopods or larvapods). Their structure is varied, though typically (e.g., in caterpillars) three regions can be distinguished: a basal membranous articulation, followed by a longer section having a sclerotized plate on the outer wall, and an apical protractile lobe, the planta, which bears claws, crochets, peripherally. The planta is protracted by means of blood pressure. Immediately above the leg there is a swollen area in the body wall, the suprapedal lobe.

Gills. A large number of aquatic larvae possess segmentally arranged gills on a varied number of abdominal segments. These are flattened, filamentous structures, frequently articulated at the base (Figure 3.35B).

Non-Segmental Appendages. In many insects non-segmental structures are present. These are typically a mediodorsal projection on the last abdominal segment. Examples of such structures are the median lamella of zygopteran larvae and the caudal filament of Microcoryphia, Zygentoma, and Ephemeroptera. Occasionally these structures are paired (e.g., the urogomphi of some larval Coleoptera) and are easily mistaken for cerci. The anal papillae of certain dipteran larvae also fit in this category.

6. Literature

Many books and review articles deal with more or less specific aspects of external structure, for example, Snodgrass (1935) [general morphology); DuPorte (1957), Snodgrass (1960), Matsuda (1965) [head]; Matsuda (1963) [thorax]; Schneider (1964), Zacharuk (1985) [antennae]; Matsuda (1976) [abdomen]; Snodgrass (1957), Scudder (1971) [male external genitalia]; Scudder (1961, 1971) [ovipositor]. Care must be taken when reading papers that deal with morphology because authors may use differing terminology and have differing views on the homology of structures.

Bitsch, J., 1994, The morphological groundplan of Hexapoda: Critical review of recent concepts, Ann. Soc. Entomol. Fr. (N.S.) 30:103-129.

Comstock, J. H., 1918, The Wings of Insects, Comstock, Ithaca, NY.

DuPorte, E. M., 1957, The comparative morphology of the insect head, Annu. Rev. Entomol. 2:55-70.

Hamilton, K. G. A., 1972a,b, The insect wing, Parts II and III, J. Kans. Entomol. Soc. 45:54-58, 145-162.

Hinton, H. E., 1955, On the structure, function, and distribution of the prolegs of Panorpoidea, with a criticism of the Berlese-Imms theory, Trans. R. Entomol. Soc. Lond. 106:455-545.

Kukalova-Peck, J., 1987, New Carboniferous Diplura, Monura, and Thysanura, the hexapod ground plan, and the role of thoracic side lobes in the origin of wings (Insecta), Can. J. Zool. 65:2327-2345.

Kukalova-Peck, J., 1991, Fossil history and the evolution of hexapod structures, in: The Insects of Australia, 2nd ed., Vol. I (CSIRO, ed.), Melbourne University Press, Carlton, Victoria.

Kukalova-Peck, J., 1992, The "Uniramia" do not exist: The ground plan of the Pterygota as revealed by Permian Diaphanopterodea from Russia (Insecta: Paleodictyopteroidea), Can. J. Zool. 70:236-255.

Kukalova-Peck, J., 1998, Arthropod phylogeny and 'basal' morphological structures, in: Arthropod Relationships (R. A. Fortey and R. H. Thomas, eds.), Chapman and Hall, London.

Lawrence, J. F., Nielsen, E. S., and Mackerras, I. M., 1991, Skeletal anatomy and key to orders, in: The Insects of Australia, 2nd ed., Vol. 1 (CSIRO, ed.), Melbourne University Press, Carlton, Victoria.

Matsuda, R., 1963, Some evolutionary aspects of the insect thorax, Annu. Rev. Entomol. 8:59-76.

Matsuda, R., 1965, Morphology and evolution of the insect head, Mem. Am. Entomol. Inst. (Ann Arbor) 4:334 pp.

Matsuda, R., 1976, Morphology and Evolution of the Insect Abdomen, Pergamon Press, Elmsford, NY.

Ragge, D. R., 1955. The Wing-Venation of the Orthoptera Saltatoria, British Museum, London.

Rempel, J. G., 1975, The evolution of the insect head: The endless dispute, Quaest. Entomol. 11:7-25.

Rempel, J. G., and Church, N. S., 1971, The embryology of Lytta viridana Le Conte (Coleoptera: Meloidae) VII. Eighty-eight to 132 h: The appendages, the cephalic apodemes, and head segmentation, Can. J. Zool. 49:1571-1581.

Schneider, D., 1964, Insect antennae, Annu. Rev. Entomol. 9:103-122.

Scholtz, G., 1998, Cleavage, germ band formation and head segmentation: The ground pattern of the Euarthropoda, in: Arthropod Relationships (R. A. Fortey and R. H. Thomas, eds.), Chapman and Hall, London.

Scudder, G. G. E., 1961, The comparative morphology of the insect ovipositor, Trans. R. Entomol. Soc. Lond. 113:25-40.

Scudder, G. G. E., 1971, Comparative morphology of insect genitalia, Annu. Rev. Entomol. 16:379-406.

Snodgrass, R. E., 1935, Principles of Insect Morphology, McGraw-Hill, New York. (Reprinted 1993, Cornell University Press.)

Snodgrass, R. E., 1957, A revised interpretation of the external reproductive organs of male insects, Smithson. Misc. Collect. 135:60 pp.

Snodgrass, R. E., 1960, Facts and theories concerning the insect head, Smithson. Misc. Collect. 142:61 pp.

Tillyard, R. J., 1918, The panorpoid complex. Part I—The wing-coupling apparatus, with special reference to the Lepidoptera, Proc. Linn. Soc. N.S.W. 43:286-319.

Tuxen, S. L., 1970, Taxonomist's Glossary of Genitalia in Insects, 2nd ed., Munksgaard, Copenhagen.

Wootton, R. J., 1979, Function, homology and terminology in insect wings, Syst. Entomol. 4:81-93.

Wootton, R. J., 1992, Functional morphology of wings, Annu. Rev. Entomol. 37:113-140.

Zacharuk, R. Y., 1985, Antennae and sensilla, in: Comprehensive Insect Physiology, Biochemistry, and Pharmacology, Vol. 6 (G. A. Kerkut and L. I. Gilbert, eds.), Pergamon Press. Elmsford, NY.

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