''Aonidiella aurantii'' or red scale is an armored
scale insect
Scale insects are small insects of the order Hemiptera, suborder Sternorrhyncha. Of dramatically variable appearance and extreme sexual dimorphism, they comprise the infraorder Coccomorpha which is considered a more convenient grouping than th ...
and a major
pest
Pest or The Pest may refer to:
Science and medicine
* Pest (organism), an animal or plant deemed to be detrimental to humans or human concerns
** Weed, a plant considered undesirable
* Infectious disease, an illness resulting from an infection
** ...
of
citrus
''Citrus'' is a genus of flowering trees and shrubs in the rue family, Rutaceae. Plants in the genus produce citrus fruits, including important crops such as oranges, lemons, grapefruits, pomelos, and limes. The genus ''Citrus'' is nati ...
. It is thought to be a native of South China but has been widely dispersed by the agency of man through the movement of infected plant material. In the United States it is known as California red scale. It was first found in California between 1868 and 1875, apparently brought there on planting material imported from Australia.
Description

The female scale insect has a circular, brownish-red cover about 1.8 millimetres in diameter. It is firmly attached to the surface when the female is moulting or reproducing. The insect itself is visible through the cover and has an oval body which becomes kidney-shaped at the last
instar
An instar (, from the Latin '' īnstar'', "form", "likeness") is a developmental stage of arthropods, such as insects, between each moult (''ecdysis''), until sexual maturity is reached. Arthropods must shed the exoskeleton in order to grow o ...
stage. The female molts twice, exuding the material from which the cover is formed and developing a concentric ring in the center each time.
There is a characteristic whitish coating on the underside of the body which separates it from the host plant.
The female is viviparous with the eggs hatching internally.
[Parry-Jones, E., 1936. "Bionomics and ecology of red scale in Southern Rhodesia". ''Publication Mazoe Citrus Experimental Station'' 5: 11–52.] She produces 100 to 150 young altogether and live nymphs or crawlers emerge from under their mother's cover at the rate of two to three per day. When they first hatch the nymphs are a yellowish color and search for a suitable place to settle in depressions on twigs, leaves or fruits. They then start feeding by inserting their mouthparts deep into the plant tissue and sucking sap from the
parenchyma
Parenchyma () is the bulk of functional substance in an animal organ or structure such as a tumour. In zoology it is the name for the tissue that fills the interior of flatworms.
Etymology
The term ''parenchyma'' is New Latin from the word π ...
cells. The saliva they inject is very toxic to the leaves, twigs, branches and fruit of citrus trees.
[Bedford, E. C. G., 1998. "Red scale ''Aonidiella auranii'' (Maskell)". In: E. C. G. Bedford, M.A. Van den Berg and E. A. De Villiers (eds.), ''Citrus pests in the Republic of South Africa''. Dynamic Ad., Nelspruit, South Africa: 132–134.] They soon begin to develop their own round, waxy covers.
[
The male scale insect develops similarly until after the second moult when it becomes oval and darker than the female, measuring about one millimetre in diameter with an eccentric cover. The adult male is a small, yellowish two-winged insect that emerges from under its elongated cover after four molts. It lives for about 6 hours and its sole purpose is to mate.][ It locates unmated females by detecting the ]pheromone
A pheromone () is a secreted or excreted chemical factor that triggers a social response in members of the same species. Pheromones are chemicals capable of acting like hormones outside the body of the secreting individual, to affect the behavio ...
s they release.
Damage and control
Red scale is potentially a severe pest of citrus in California, Australia, New Zealand, Mexico, Chile, Argentina, Brazil, Israel, the eastern Mediterranean islands, and South Africa.[
Although citrus is the main crop attacked by red scale, it can also be found on species from at least seventy-seven plant families and has been successfully reared in the laboratory on potato tubers and pumpkin. Scale insects of all ages feed by sucking ]sap
Sap is a fluid transported in xylem cells (vessel elements or tracheids) or phloem sieve tube elements of a plant. These cells transport water and nutrients throughout the plant.
Sap is distinct from latex, resin, or cell sap; it is a separ ...
. They are found on all parts of the plant but are most noticeable on the fruit. Heavy infestations may cause discoloration, shoot distortion and leaf drop. The fruit may become pitted and unmarketable. The tree's bark may split and the twigs and branches may die back and this sometimes results in the death of the tree. Chemical control is difficult because the insects are protected by their hard waxy covers. They are also becoming resistant to many insecticides and indiscriminate use of pesticides has adverse effects on their natural predators.[
Some ant species can increase infestations of red scale indirectly. By patrolling the branches in search of honeydew from soft scales, ]cottony cushion scale
''Icerya purchasi'' (common name: cottony cushion scale) is a scale insect that feeds on more than 80 families of woody plants, most notably on ''Citrus'' and ''Pittosporum''. Originally described in 1878 from specimens collected in New Zealand ...
, mealybug
Mealybugs are insects in the family Pseudococcidae, unarmored scale insects found in moist, warm habitats. Many species are considered pests as they feed on plant juices of greenhouse plants, house plants and subtropical trees and also act as a ...
s and aphid
Aphids are small sap-sucking insects and members of the superfamily Aphidoidea. Common names include greenfly and blackfly, although individuals within a species can vary widely in color. The group includes the fluffy white woolly aphids. A ...
s, they deter predator
Predation is a biological interaction where one organism, the predator, kills and eats another organism, its prey. It is one of a family of common feeding behaviours that includes parasitism and micropredation (which usually do not kill ...
s and parasitoids and thus enable red scale to flourish unmolested. The only mobile stage of red scale is the first instar crawler. It can move about a metre but may also be dispersed to other plants by wind, flying insects and birds as well as human activities.
Other crops that suffer economic damage from attack by red scale include papaya
The papaya (, ), papaw, () or pawpaw () is the plant species ''Carica papaya'', one of the 21 accepted species in the genus '' Carica'' of the family Caricaceae. It was first domesticated in Mesoamerica, within modern-day southern Mexico and ...
(''Carica papaya'') in Taiwan, guava
Guava () is a common tropical fruit cultivated in many tropical and subtropical regions. The common guava '' Psidium guajava'' (lemon guava, apple guava) is a small tree in the myrtle family (Myrtaceae), native to Mexico, Central America, ...
(''Psidium guajava'') in India and olive
The olive, botanical name ''Olea europaea'', meaning 'European olive' in Latin, is a species of small tree or shrub in the family Oleaceae, found traditionally in the Mediterranean Basin. When in shrub form, it is known as ''Olea europaea'' ...
s in California and countries around the Mediterranean, with serious damage being caused to olives in Morocco.
Natural enemies of red scale vary in the different parts of the world in which it is found. Parasitoids include '' Aphelinus africanus'', several species of ''Aphytis
Aphytis ( grc, Ἄφυτις), also Aphyte (Ἀφύτη) and Aphytus or Aphytos (Ἄφυτος), was an ancient Greek city in Pallene, the westernmost headland of Chalcidice. Around the middle of the 8th century BC colonists from Euboea arrive ...
'', ''Comperiella bifasciata
''Comperiella bifasciata'' is a parasitic wasp species in the genus '' Comperiella'' in the family Encyrtidae. It is used in biological control of California red scale and yellow scale of citrus.
Description
''Comperiella bifasciata'' is a ti ...
'', species of '' Encarsia'', '' Habrolepis rouxi'' and '' Signiphora fax''.[ Predators include '' Aleurodothrips fasciapennis'', several species of '' Chilocorus'', '' Cybocephalus micans'', '' Cryptolaemus montrouzieri'', '' Hemisarcoptes malus'' and '' Rhyzobius lophanthae''.][
In California, several predators feed on red scale including the lady beetles, '' Rhyzobius lophanthae'', '' Chilocorus orbus'' and '' Chiliocorus cacti''. The naturally occurring parasitic wasps, '']Aphytis melinus
''Aphytis melinus'' is an internal parasite of the California red scale, ''Aonidiella aurantii'', which is a pest of citrus in California and elsewhere. This wasp drums its antennae against the scale insect to find out if it is healthy, if it is ...
'', ''Aphytis lingnanensis
Aphytis ( grc, Ἄφυτις), also Aphyte (Ἀφύτη) and Aphytus or Aphytos (Ἄφυτος), was an ancient Greek city in Pallene, the westernmost headland of Chalcidice. Around the middle of the 8th century BC colonists from Euboea arrived ...
'' and ''Comperiella bifasciata
''Comperiella bifasciata'' is a parasitic wasp species in the genus '' Comperiella'' in the family Encyrtidae. It is used in biological control of California red scale and yellow scale of citrus.
Description
''Comperiella bifasciata'' is a ti ...
'' also play a part in controlling red scale on citrus but their ability to do so depends on the selective use of insecticides for other pests. Careful monitoring of the host plants will indicate whether release of captive-bred ''Aphytis melinus'' is necessary and the use of pesticides should be minimized before this is done. Ants, especially the Argentine ant, ''Linepithema humile
The Argentine ant (''Linepithema humile''), formerly ''Iridomyrmex humilis'', is an ant native to northern Argentina, Uruguay, Paraguay, Bolivia and southern Brazil. It is an invasive species that has been established in many Mediterranean climat ...
'', and the native gray ant should also be controlled as they disrupt the predation of the scale insects by the wasp.[
In Australia, the parasitic wasp '']Aphytis lingnanensis
Aphytis ( grc, Ἄφυτις), also Aphyte (Ἀφύτη) and Aphytus or Aphytos (Ἄφυτος), was an ancient Greek city in Pallene, the westernmost headland of Chalcidice. Around the middle of the 8th century BC colonists from Euboea arrived ...
'' is used for biological pest control
Biological control or biocontrol is a method of controlling pests, such as insects, mites, weeds, and plant diseases, using other organisms. It relies on predation, parasitism, herbivory, or other natural mechanisms, but typically also i ...
. It is usually released annually as, although the wasps may build up naturally without being released, the life cycle is not well synchronized with the pest and significant populations of scale insect may build up before many wasps are available.
References
External links
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{{Taxonbar, from=Q3620551
Agricultural pest insects
Citrus pests
Insects of Asia
Aspidiotina