Scale insect
Overview
The scale insects are small insect
Insect
Insects are a class of living creatures within the arthropods that have a chitinous exoskeleton, a three-part body , three pairs of jointed legs, compound eyes, and two antennae...

s of the order Hemiptera
Hemiptera
Hemiptera is an order of insects most often known as the true bugs , comprising around 50,000–80,000 species of cicadas, aphids, planthoppers, leafhoppers, shield bugs, and others...

, generally classified as the superfamily
Taxonomic rank
In biological classification, rank is the level in a taxonomic hierarchy. Examples of taxonomic ranks are species, genus, family, and class. Each rank subsumes under it a number of less general categories...

 Coccoidea. There are about 8,000 species of scale insects.
Most scale insects are parasites of plant
Plant
Plants are living organisms belonging to the kingdom Plantae. Precise definitions of the kingdom vary, but as the term is used here, plants include familiar organisms such as trees, flowers, herbs, bushes, grasses, vines, ferns, mosses, and green algae. The group is also called green plants or...

s, feeding on sap
Sap
Sap may refer to:* Plant sap, the fluid transported in xylem cells or phloem sieve tube elements of a plant* Sap , a village in the Dunajská Streda District of Slovakia...

 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
Newsteadia
Newsteadia is a genus of ensign scale insects in the superfamily Coccoidea. Most species are inconspicuous, measureing under two millimeters long and found in leaf litter.-Species:...

in the family Ortheziidae. Scale insects vary dramatically in their appearance from very small organisms (1–2 mm) that occur under wax covers (some look like oyster shells), to shiny pearl-like objects (about 5 mm), to creatures covered with mealy wax.
Encyclopedia
The scale insects are small insect
Insect
Insects are a class of living creatures within the arthropods that have a chitinous exoskeleton, a three-part body , three pairs of jointed legs, compound eyes, and two antennae...

s of the order Hemiptera
Hemiptera
Hemiptera is an order of insects most often known as the true bugs , comprising around 50,000–80,000 species of cicadas, aphids, planthoppers, leafhoppers, shield bugs, and others...

, generally classified as the superfamily
Taxonomic rank
In biological classification, rank is the level in a taxonomic hierarchy. Examples of taxonomic ranks are species, genus, family, and class. Each rank subsumes under it a number of less general categories...

 Coccoidea. There are about 8,000 species of scale insects.

Ecology

Most scale insects are parasites of plant
Plant
Plants are living organisms belonging to the kingdom Plantae. Precise definitions of the kingdom vary, but as the term is used here, plants include familiar organisms such as trees, flowers, herbs, bushes, grasses, vines, ferns, mosses, and green algae. The group is also called green plants or...

s, feeding on sap
Sap
Sap may refer to:* Plant sap, the fluid transported in xylem cells or phloem sieve tube elements of a plant* Sap , a village in the Dunajská Streda District of Slovakia...

 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
Newsteadia
Newsteadia is a genus of ensign scale insects in the superfamily Coccoidea. Most species are inconspicuous, measureing under two millimeters long and found in leaf litter.-Species:...

in the family Ortheziidae. Scale insects vary dramatically in their appearance from very small organisms (1–2 mm) that occur under wax covers (some look like oyster shells), to shiny pearl-like objects (about 5 mm), to creatures covered with mealy wax. Adult female scales are almost always immobile (aside from mealybug
Mealybug
Mealybugs are insects in the family Pseudococcidae, unarmored scale insects found in moist, warm climates. They are considered pests as they feed on plant juices of greenhouse plants, house plants and subtropical trees and also acts as a vector for several plant diseases.-Distribution:Mealybugs...

s) and permanently attached to the plant they have parasitized. They secrete a wax
Wax
thumb|right|[[Cetyl palmitate]], a typical wax ester.Wax refers to a class of chemical compounds that are plastic near ambient temperatures. Characteristically, they melt above 45 °C to give a low viscosity liquid. Waxes are insoluble in water but soluble in organic, nonpolar solvents...

y coating for defense; this coating causes them to resemble reptilian scales or fish scales
Scale (zoology)
In most biological nomenclature, a scale is a small rigid plate that grows out of an animal's skin to provide protection. In lepidopteran species, scales are plates on the surface of the insect wing, and provide coloration...

, hence the name.

Scale insects feed on a wide variety of plant
Plant
Plants are living organisms belonging to the kingdom Plantae. Precise definitions of the kingdom vary, but as the term is used here, plants include familiar organisms such as trees, flowers, herbs, bushes, grasses, vines, ferns, mosses, and green algae. The group is also called green plants or...

s, and many scale species are considered pest
Pest (animal)
A pest is an animal which is detrimental to humans or human concerns. It is a loosely defined term, often overlapping with the related terms vermin, weeds, parasites and pathogens...

s. Some types are economically valuable, such as the cochineal
Cochineal
The cochineal is a scale insect in the suborder Sternorrhyncha, from which the crimson-colour dye carmine is derived. A primarily sessile parasite native to tropical and subtropical South America and Mexico, this insect lives on cacti from the genus Opuntia, feeding on plant moisture and...

, Polish cochineal
Polish cochineal
Polish cochineal , also known as Polish carmine scales, is a scale insect formerly used to produce a crimson dye of the same name, colloquially known as "Saint John's blood". The larvae of P...

 and lac scales. Scale insects' waxy covering makes them quite resistant to pesticide
Pesticide
Pesticides are substances or mixture of substances intended for preventing, destroying, repelling or mitigating any pest.A pesticide may be a chemical unicycle, biological agent , antimicrobial, disinfectant or device used against any pest...

s, which are only effective against the first-instar
Instar
An instar is a developmental stage of arthropods, such as insects, between each molt , until sexual maturity is reached. Arthropods must shed the exoskeleton in order to grow or assume a new form. Differences between instars can often be seen in altered body proportions, colors, patterns, or...

 nymph
Nymph (biology)
In biology, a nymph is the immature form of some invertebrates, particularly insects, which undergoes gradual metamorphosis before reaching its adult stage. Unlike a typical larva, a nymph's overall form already resembles that of the adult. In addition, while a nymph moults it never enters a...

 crawler stage. However, scales are often controlled with horticultural oil
Horticultural oil
Horticultural Oils or Narrow Range Oils are lightweight oils, either petroleum or vegetable based. They are used in both horticulture and agriculture, where they are applied as a dilute spray on plant surfaces to control insects and mites...

s, which suffocate
Suffocation
Suffocation is the process of Asphyxia.Suffocation may also refer to:* Suffocation , an American death metal band* "Suffocation", a song on Morbid Angel's debut album, Altars of Madness...

 them, or through biological control.

Some scale insects species evolved symbiotically with some ant species.

Description

Scale insects show very great sexual dimorphism. Female scale insects, unusually for Hemiptera, retain the immature external morphology at sexual maturity (neoteny
Neoteny
Neoteny , also called juvenilization , is one of the two ways by which paedomorphism can arise. Paedomorphism is the retention by adults of traits previously seen only in juveniles, and is a subject studied in the field of developmental biology. In neoteny, the physiological development of an...

). Adult males can have wings but never feed and die within a day or two. Male scale insects may or may not have wings, depending on their species. Species in which males do have wings are unusual among insects, in that they generally possess only one pair of fully functional wings. In this they resemble true flies
Fly
True flies are insects of the order Diptera . They possess a pair of wings on the mesothorax and a pair of halteres, derived from the hind wings, on the metathorax...

 (Diptera). However, their tail filaments do not resemble anything in the morphology of flies. Their hind (metathoracic
Metathorax
The metathorax is the posterior of the three segments in the thorax of an insect, and bears the third pair of legs. Its principal sclerites are the metanotum , the metasternum , and the metapleuron on each side...

) wings 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, which usually is a condition associated with the Hymenoptera
Hymenoptera
Hymenoptera is one of the largest orders of insects, comprising the sawflies, wasps, bees and ants. There are over 130,000 recognized species, with many more remaining to be described. The name refers to the heavy wings of the insects, and is derived from the Ancient Greek ὑμήν : membrane and...

. The vestigial wings often are reduced to the point where they are referred to as halteres
Halteres
Halteres are small knobbed structures modified from the hind wings in some two-winged insects. They are flapped rapidly and function as gyroscopes, informing the insect about rotation of the body during flight....

 or pseudohalteres. It is not at present clear to what extent the pseudohalteres have any substantial control function to match the true halteres of the flies
Diptera
Diptera , or true flies, is the order of insects possessing only a single pair of wings on the mesothorax; the metathorax bears a pair of drumstick like structures called the halteres, the remnants of the hind wings. It is a large order, containing an estimated 240,000 species, although under half...

.

The specifics of their reproductive systems vary considerably within the group, including hermaphroditism and at least seven forms of parthenogenesis
Parthenogenesis
Parthenogenesis is a form of asexual reproduction found in females, where growth and development of embryos occur without fertilization by a male...

.

Systematics

The main families of scale insects are:
  • Margarodidae
    Margarodidae
    Margarodidae is a family of scale insects within superfamily Coccoidea. Members of the family include giant coccids , Polish cochineal and ground pearls ....

     – cottony cushion scales, giant coccids and ground pearls
  • Diaspididae
    Diaspididae
    Diaspididae is the largest family of scale insects with over 2650 described species in around 400 genera. As with all scale insects, the female produces a waxy protective scale beneath which it feeds on its host plant...

     – armored scales
  • Dactylopiidae
    Cochineal
    The cochineal is a scale insect in the suborder Sternorrhyncha, from which the crimson-colour dye carmine is derived. A primarily sessile parasite native to tropical and subtropical South America and Mexico, this insect lives on cacti from the genus Opuntia, feeding on plant moisture and...

     – cochineal
  • Kerriidae
    Kerriidae
    Kerriidae is a family of scale insects known as lac scales.Species include:*Kerria lacca - true lac scale*Paratachardina decorella - rosette lac scale*Paratachardina pseudolobata - lobate lac scale-References:...

     – lac scales
  • Coccidae
    Coccidae
    The Coccidae are a family of scale insects belonging to the superfamily Coccoidea. They are commonly known as soft scales, wax scales or tortoise scales. The females are flat with elongated oval bodies and a smooth integument which may be covered with wax. In some genera they possess legs but in...

     – soft scales
  • Asterolecaniidae
    Asterolecaniidae
    Asterolecaniidae is a family of scale insects commonly known as pit scales or asterolecaniids. They typically cause a depression in the host plant's tissues and often cause distortion of the shoots. They are found on a range of hosts but are especially common on oaks, bamboos and a number of...

     – pit scales
  • Pseudococcidae
    Mealybug
    Mealybugs are insects in the family Pseudococcidae, unarmored scale insects found in moist, warm climates. They are considered pests as they feed on plant juices of greenhouse plants, house plants and subtropical trees and also acts as a vector for several plant diseases.-Distribution:Mealybugs...

     – mealybugs
  • Eriococcidae
    Eriococcidae
    Eriococcidae is a family of scale insects in the order Hemiptera. They are commonly known as felt scales or eriococcids. Each species is usually specific to a different plant host....

     – felted scales


A number of other families are known only from fossil
Fossil
Fossils are the preserved remains or traces of animals , plants, and other organisms from the remote past...

s, including Arnoldidae, Electrococcidae, Grimaldiellidae, Grohnidae, Hammanococcidae, Inkaidae, Jersicoccidae, Kukaspididae, Labiococcidae, Lebanococcidae, Lithuanicoccidae, Pennygullaniidae, Serafinidae and Weitschatidae.

External links



On the University of Florida
University of Florida
The University of Florida is an American public land-grant, sea-grant, and space-grant research university located on a campus in Gainesville, Florida. The university traces its historical origins to 1853, and has operated continuously on its present Gainesville campus since September 1906...

 / Institute of Food and Agricultural Sciences
Institute of Food and Agricultural Sciences
The University of Florida’s Institute of Food and Agricultural Sciences is a federal-state-county partnership dedicated to developing knowledge in agriculture, human and natural resources, and the life sciences, and enhancing and sustaining the quality of human life by making that information...

Featured Creatures website:
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