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Brief Summary

    Scale insect: Brief Summary
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    The scale insects are small insects of the order Hemiptera, suborder Sternorrhyncha. They comprise the superfamily Coccoidea, previously placed in the now obsolete group called "Homoptera". There are about 8,000 described species of scale insects.

     src= Armored scale insects:(A) Lepidosaphes gloverii, adult females. (B) Parlatoria oleae, adult females (circular, with dark spot) and immatures (oblong). (C) Diaspidiotus juglansregiae, adult female walnut scale with waxy scale cover removed.  src= Oystershell scale (Ceroplastes sp.), a waxy scale on young blueberry
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    Brief Summary
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    Coccoidea or scale insects is a large superfamily in the order Hemiptera with a worldwide distribution. They are unusually small insects, highly specialized for plant parasitism, that have evolved different kinds of metamorphosis depending on sex and family. Scale insects are characterized by sexual dimorphism: females are wingless, usually small (from 0.5 – 10 mm), with an oval or round but flat to fairly convex body form, sometimes bud shaped, and often protected by waxy secretions or covers. The adult females may exhibit reduction or loss of appendages, depending on family and instar, and are often sedentary or sessile. Adult males are usually winged and inconspicuous, do not feed and live a few days. Scale insect identification is mainly based upon the morphology of adult females that persist on the host plant longer than the other stages.

    Females usually take three or four developmental stages to reach maturity, males usually five. Parthenogenesis is quite common. Eggs are usually laid under the female body, under the scale cover, or in waxy egg-sacs. Dispersal is carried out by first instars.

    Scale insects feed on various parts of the host plant (leaves, fruits, stems, branches and roots) and are frequently introduced and acclimatized in different parts of the world. This is due to their small size (first instars are about 0.2–0.3 mm; adult females usually are from 0.5 to10 mm long) and their concealment using waxy secretions; beside many species live in hidden habitats (under leaf sheaths, in bark crevices or on roots) so that they can easily escape visual quarantine inspections. Once in a new territory, parthenogenesis and high fecundity favour quick colonization starting from a few females: for example, a single female Neopulvinaria innumerabilis may lay up to 8000 eggs (Canard 1968).

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    Giuseppina Pellizzari & Jean-François Germain
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    Pellizzari G, Germain J-F (2010) Scales (Hemiptera, Superfamily Coccoidea). Chapter 9.3. In: Roques A et al. (Eds) Alien terrestrial arthropods of Europe. BioRisk 4(1): 475–510. doi: 10.3897/biorisk.4.45
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    Katja Schulz (Katja)
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Comprehensive Description

    Scale insect
    provided by wikipedia

    The scale insects are small insects of the order Hemiptera, suborder Sternorrhyncha. They comprise the superfamily Coccoidea, previously placed in the now obsolete group called "Homoptera". There are about 8,000 described species of scale insects.

     src=
    Armored scale insects:(A) Lepidosaphes gloverii, adult females. (B) Parlatoria oleae, adult females (circular, with dark spot) and immatures (oblong). (C) Diaspidiotus juglansregiae, adult female walnut scale with waxy scale cover removed.
     src=
    Oystershell scale (Ceroplastes sp.), a waxy scale on young blueberry

    Description

    Scale insects vary dramatically in appearance; from very small organisms (1–2 mm) that grow beneath wax covers (some shaped like oyster shells, others like mussel shells), to shiny pearl-like objects (about 5 mm), to creatures covered with mealy wax. Adult female scales are almost always immobile (aside from mealybugs) and permanently attached to the plant they have parasitized. They secrete a waxy coating for defense; this coating causes them to resemble reptilian scales or fish scales, hence their common name.

    The group shows high degrees of sexual dimorphism; female scale insects, unusually for Hemiptera, retain the immature external morphology even when sexually mature, a condition known as neoteny. Adult males usually have wings (depending on their species) but never feed, and die within a day or two.

    Species in which males do have wings generally possess only one pair of fully functional wings, and in particular, the forewings. This is unusual among insects; it most closely resembles the situation in the true flies, the Diptera. However, the Diptera and Hemiptera are not at all closely related and do not closely resemble each other in morphology; for example, the tail filaments of the Coccoidea do not resemble anything in the morphology of flies. The hind (metathoracic) wings of scale insects are reduced, commonly to the point that they generally are overlooked. In some species the hind wings have hamuli, hooklets, that couple the hind wings to the main wings, a condition usually associated with the Hymenoptera. The vestigial wings often are reduced to the point where they are referred to as halteres or pseudohalteres, but again, their resemblance to the halteres of flies is analogous, not homologous.[2] It is not at present clear to what extent the pseudohalteres have any substantial control function to match the true halteres of the flies.

    The first instars of most species of scale insects emerge from the egg with functional legs and are informally called "crawlers". They immediately crawl around in search of a favorable spot to settle down and feed. In some species they delay settling down either until they are starving, or until they have been blown away by wind onto what presumably is another plant, where they may establish a colony separate from the parent. There are many variations on such themes, such as scale insects that are associated with species of ants that act as herders and carry the young ones to favorable protected sites to feed. In either case, many such species of crawlers, when they change their skins, lose the use of their legs if they are female, and stay put for life. Only the males retain their legs and use them in seeking females for mating.[3]

    The specifics of their reproductive systems vary considerably within the group, including three forms of hermaphroditism[4] and at least seven forms of parthenogenesis.[citation needed]

    Ecology

    Most scale insects are parasites of plants, feeding on sap drawn directly from the plant's vascular system. A few species feed on fungal mats and fungi, e.g., some species in the genus Newsteadia in the family Ortheziidae.

    Scale insects feed on a wide variety of plants, though particular species commonly are specific to particular host plants or plant groups. For example, various kinds of cochineal are restricted to cactus hosts. Some scale insect species evolved symbiotically with some ant species.[5]

    Economic significance

    Many scale species are serious crop pests. The waxy covering of many species of scale insects protects them effectively from contact insecticides, which are only effective against the first-instar nymph stage known as the crawler. However, scales often are controlled by use of horticultural oils, that suffocate them, systemic pesticides that poison the sap of the host plants, or by biological control agents such as tiny parasitoid wasps and Coccinellid beetles. Insecticidal soap may also be used against scales. It is commercially available or can be made of certain types of household soap.

    At the same time, some kinds of scale insects are biological control agents for pest plants, such as various species of Dactylopius, the cochineal genus, that attack invasive species of Opuntia.

    Some types of scale insect are economically valuable for the substances they can yield under proper husbandry. Some, such as the cochineal, kermes, lac, Armenian cochineal, and Polish cochineal have been used to produce red dyes for coloring foods and dyeing fabrics. Some waxy scale species in the genera Ceroplastes and Ericerus produce materials such as Chinese wax, and several genera of lac scales produce shellac.

    Systematics

    Recognition of various scale insect families has fluctuated over time, and the validity of many remain in flux. The major subdivision is between the more ancient forms, the archaeococcoids, and the more recently emerged forms, the neococcoids. The main families of scale insects are:[6][7]

    A number of other families are known only from fossils, including Albicoccidae, Burmacoccidae, Arnoldidae, Electrococcidae, Grimaldiellidae, Grohnidae, Hammanococcidae, Inkaidae, Jersicoccidae, Kukaspididae, Labiococcidae, Lebanococcidae, Lithuanicoccidae, Pennygullaniidae, Serafinidae and Weitschatidae.[8][9]

    See also

    References

    1. ^ "Coccoidea Handlirsch, 1903". Integrated Taxonomic Information System..mw-parser-output cite.citation{font-style:inherit}.mw-parser-output q{quotes:"""""'"'"}.mw-parser-output code.cs1-code{color:inherit;background:inherit;border:inherit;padding:inherit}.mw-parser-output .cs1-lock-free a{background:url("//upload.wikimedia.org/wikipedia/commons/thumb/6/65/Lock-green.svg/9px-Lock-green.svg.png")no-repeat;background-position:right .1em center}.mw-parser-output .cs1-lock-limited a,.mw-parser-output .cs1-lock-registration a{background:url("//upload.wikimedia.org/wikipedia/commons/thumb/d/d6/Lock-gray-alt-2.svg/9px-Lock-gray-alt-2.svg.png")no-repeat;background-position:right .1em center}.mw-parser-output .cs1-lock-subscription a{background:url("//upload.wikimedia.org/wikipedia/commons/thumb/a/aa/Lock-red-alt-2.svg/9px-Lock-red-alt-2.svg.png")no-repeat;background-position:right .1em center}.mw-parser-output .cs1-subscription,.mw-parser-output .cs1-registration{color:#555}.mw-parser-output .cs1-subscription span,.mw-parser-output .cs1-registration span{border-bottom:1px dotted;cursor:help}.mw-parser-output .cs1-hidden-error{display:none;font-size:100%}.mw-parser-output .cs1-visible-error{font-size:100%}.mw-parser-output .cs1-subscription,.mw-parser-output .cs1-registration,.mw-parser-output .cs1-format{font-size:95%}.mw-parser-output .cs1-kern-left,.mw-parser-output .cs1-kern-wl-left{padding-left:0.2em}.mw-parser-output .cs1-kern-right,.mw-parser-output .cs1-kern-wl-right{padding-right:0.2em}
    2. ^ Scholtz, C. H. (1985). Insects of southern Africa. London: Butterworths. ISBN 0-409-10487-6.[page needed]
    3. ^ Richards, O. W.; Davies, R.G. (1977). Imms' General Textbook of Entomology: Volume 1: Structure, Physiology and Development Volume 2: Classification and Biology. Berlin: Springer. ISBN 0-412-61390-5.[page needed]
    4. ^ Gardner, A.; Ross, L. (2011). "The Evolution of Hermaphroditism by an Infectious Male-Derived Cell Lineage: An Inclusive-Fitness Analysis". The American Naturalist. 178 (2): 191–201. doi:10.1086/660823. PMID 21750383.
    5. ^ Itino, Takao; Murase, Kaori; Sato, Yumiko; Inamori, Keita; Itioka, Takao; Quek, Swee-Peck; Ueda, Shouhei (2008). "An ancient tripartite symbiosis of plants, ants and scale insects". Proceedings of the Royal Society B: Biological Sciences. 275 (1649): 2319–26. doi:10.1098/rspb.2008.0573. JSTOR 25249807. PMC 2603224. PMID 18611850.
    6. ^ Gullan, P. J. & Cook, L. G. (2007). "Phylogeny and higher classification of the scale insects (Hemiptera: Sternorrhyncha: Coccoidea)". Zootaxa. 1668: 413–425.
    7. ^ Hodgson, Chris J. & Hardy, Nate B. (2013). "The phylogeny of the superfamily Coccoidea (Hemiptera: Sternorrhyncha) based on the morphology of extant and extinct macropterous males". Systematic Entomology. 38 (4): 794–804. doi:10.1111/syen.12030. Archived from the original on 29 December 2013.
    8. ^ Ben-Dov, Y., Miller, D.R. & Gibson, G.A.P. ScaleNet "Archived copy". Archived from the original on 2013-04-04. Retrieved 2013-04-04.CS1 maint: Archived copy as title (link)
    9. ^ Johnson, Christine; Agosti, Donat; Delabie, Jacques H.; Dumpert, Klaus; Williams, D. J.; Tschirnhaus, Michael VON; Maschwitz, Ulrich (2001). "Acropyga and Azteca Ants (Hymenoptera: Formicidae) with Scale Insects (Sternorrhyncha: Coccoidea): 20 Million Years of Intimate Symbiosis". American Museum Novitates. 335: 1–18. doi:10.1206/0003-0082(2001)335<0001:AAAAHF>2.0.CO;2. ISSN 0003-0082.

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