Aonidiella aurantii
Encyclopedia
Aonidiella aurantii or red scale is an armoured scale insect
and a major pest of citrus
. 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 USA 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.
stage. The female moults 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. 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 colour 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
cells. The saliva they inject is very toxic to the leaves, twigs, branches and fruit of citrus trees. 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 excentric cover. The adult male is a small, yellowish two-winged insect that emerges from under its elongated cover after four moults. It lives for about 6 hours and its sole purpose is to mate. It locates unmated females by detecting the pheromone
s they release.
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
. They are found on all parts of the plant but are most noticeable on the fruit. Heavy infestations may cause discolouration, 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
, mealybug
s and aphid
s, they deter predators and parasitoid
s 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
(Carica papaya) in Taiwan, guava
(Psidium guajava) in India and olive
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
, Comperiella bifasciata, 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 lingnanensis and Comperiella bifasciata 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 minimised before this is done. Ants, especially the Argentine ant, Linepithema humile, and the native gray ant should also be controlled as they disrupt the relationship between the wasp and the scale insects.
In Australia, the parasitic wasp, Aphytis lingnanensis is used for biological pest control
. It is usually released annually as, although the wasps may build up naturally without being released, they life cycle is not well synchronized with the pest and significant populations of scale insect may build up before many wasps are available.
Scale insect
The scale insects are small insects of the order Hemiptera, generally classified as the superfamily Coccoidea. There are about 8,000 species of scale insects.-Ecology:...
and a major pest of citrus
Citrus
Citrus is a common term and genus of flowering plants in the rue family, Rutaceae. Citrus is believed to have originated in the part of Southeast Asia bordered by Northeastern India, Myanmar and the Yunnan province of China...
. 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 USA 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 instarInstar
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...
stage. The female moults 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. 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 colour 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
Parenchyma is a term used to describe a bulk of a substance. It is used in different ways in animals and in plants.The term is New Latin, f. Greek παρέγχυμα - parenkhuma, "visceral flesh", f. παρεγχεῖν - parenkhein, "to pour in" f. para-, "beside" + en-, "in" + khein, "to pour"...
cells. The saliva they inject is very toxic to the leaves, twigs, branches and fruit of citrus trees. 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 excentric cover. The adult male is a small, yellowish two-winged insect that emerges from under its elongated cover after four moults. It lives for about 6 hours and its sole purpose is to mate. It locates unmated females by detecting the pheromone
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 outside the body of the secreting individual to impact the behavior of the receiving individual...
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
Plant sap
Sap is a fluid transported in xylem cells or phloem sieve tube elements of a plant. It transports water and nutrients throughout the plant....
. They are found on all parts of the plant but are most noticeable on the fruit. Heavy infestations may cause discolouration, 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
Ant
Ants are social insects of the family Formicidae and, along with the related wasps and bees, belong to the order Hymenoptera. Ants evolved from wasp-like ancestors in the mid-Cretaceous period between 110 and 130 million years ago and diversified after the rise of flowering plants. More than...
species can increase infestations of red scale indirectly. By patrolling the branches in search of honeydew from soft scales
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...
, cottony cushion scale
Icerya purchasi
Icerya purchasi is a scale insect that feeds on several species of woody plants, most notably on Citrus and Pittosporum. Originally identified in 1878 as a New Zealand located pest of kangaroo acacia, it is now found worldwide where citrus crops are grown.-Life cycle:This scale infests twigs and...
, 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 aphid
Aphid
Aphids, also known as plant lice and in Britain and the Commonwealth as greenflies, blackflies or whiteflies, are small sap sucking insects, and members of the superfamily Aphidoidea. Aphids are among the most destructive insect pests on cultivated plants in temperate regions...
s, they deter predators and parasitoid
Parasitoid
A parasitoid is an organism that spends a significant portion of its life history attached to or within a single host organism in a relationship that is in essence parasitic; unlike a true parasite, however, it ultimately sterilises or kills, and sometimes consumes, the host...
s 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
Papaya
The papaya , papaw, or pawpaw is the fruit of the plant Carica papaya, the sole species in the genus Carica of the plant family Caricaceae...
(Carica papaya) in Taiwan, guava
Guava
Guavas are plants in the myrtle family genus Psidium , which contains about 100 species of tropical shrubs and small trees. They are native to Mexico, Central America, and northern South America...
(Psidium guajava) in India and olive
Olive
The olive , Olea europaea), is a species of a small tree in the family Oleaceae, native to the coastal areas of the eastern Mediterranean Basin as well as northern Iran at the south end of the Caspian Sea.Its fruit, also called the olive, is of major agricultural importance in the...
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
Aphytis was an ancient Greek city in Pallene, the westernmost headland of Chalcidice. Around the middle of the 8th century BC colonists from Euboea arrived. The city became well known for its Temple of Dionysus, which appears to have been built in the second half of the 8th century BC...
, Comperiella bifasciata, species of Encarsia
Encarsia
Encarsia is a large genus of minute parasitic wasps of the family Aphelinidae. The genus is very diverse with currently about 400 described species and worldwide distribution. The number of existing species is expected to be several times higher because many species are still undescribed...
, Habrolepis rouxi and Signiphora fax. Predators include Aleurodothrips fasciapennis, several species of Chilocorus, Cybocephalus micans, Cryptolaemus montrouzieri
Cryptolaemus montrouzieri
Cryptolaemus montrouzieri, common name Mealybug Ladybird is ladybird species endemic to Queensland and New South Wales, Australia. Unlike many of the often brightly-coloured Coccinellidae, it is predominantly brown and has no spots. It has been used as a biological control agent against Mealybugs...
, 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
Aphytis melinus is an internal parasite of the California Red Scale, Aonidiella aurantii, which is a pest of citrus in California and elsewhere. This chalcid wasp drums its antennae against the scale insect to find out if it is healthy, if it is already parasitized, how large it is, etc., to decide...
, Aphytis lingnanensis and Comperiella bifasciata 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 minimised before this is done. Ants, especially the Argentine ant, Linepithema humile, and the native gray ant should also be controlled as they disrupt the relationship between the wasp and the scale insects.
In Australia, the parasitic wasp, Aphytis lingnanensis is used for biological pest control
Biological pest control
Biological control of pests in agriculture is a method of controlling pests that relies on predation, parasitism, herbivory, or other natural mechanisms...
. It is usually released annually as, although the wasps may build up naturally without being released, they life cycle is not well synchronized with the pest and significant populations of scale insect may build up before many wasps are available.
External links
- California red scale
- CISR: California Red Scale Center for Invasive Species Research
- http://www.bugsforbugs.com.au/product/aphytis-red-scale-biological-control Bugs for Bugs
- http://nlbif.eti.uva.nl/bis/diaspididae.php?menuentry=soorten&id=83 Arthropods of Economic Importance:Aonidiella aurantii