Icerya purchasi (cottony cushion scale)
- Summary of Invasiveness
- Taxonomic Tree
- Notes on Taxonomy and Nomenclature
- Distribution Table
- History of Introduction and Spread
- Risk of Introduction
- Hosts/Species Affected
- Growth Stages
- List of Symptoms/Signs
- Biology and Ecology
- Natural enemies
- Notes on Natural Enemies
- Means of Movement and Dispersal
- Plant Trade
- Wood Packaging
- Impact Summary
- Impact: Biodiversity
- Detection and Inspection
- Similarities to Other Species/Conditions
- Prevention and Control
- Distribution Maps
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PicturesTop of page
IdentityTop of page
Preferred Scientific Name
- Icerya purchasi Maskell
Preferred Common Name
- cottony cushion scale
Other Scientific Names
- Pericerya purchasi (Maskell)
International Common Names
- English: Australian bug; citrus fluted scale; fluted scale; mealy scale; white scale
- Spanish: coccido acanalado; cochinilla acanalada de los agrios; cochinilla algodonosa australiana; cochinilla blanca del naranjo; escama algodonosa de los citricos (Mexico); escama harinosa; escama lanigera
- French: cochenille australienne; cochenille flûtée; cochenille l'icerya; cochenille pericerya
- Portuguese: cochonilha australiana; pulgao branco (Brasil)
Local Common Names
- Brazil: pulgão branco
- Germany: Australische wollschildlaus
- Israel: izeriat haadaim
- Italy: iceria di purchase
- Japan: iseriya-kaigaramusi
- Netherlands: geribde djeroek-luis; witte geribde schildluis
- South Africa: australiese luis
- Turkey: torbali kosnil
- ICERPU (Icerya purchasi)
Summary of InvasivenessTop of page I. purchasi extracts significant quantities of sap from the host plant. Damage is mostly caused by sap depletion; the shoots dry up, defoliation occurs and branches or whole trees may die. Copious honeydew excreted by the scales coats the leaves, resulting in sooty mould growth, which blocks light and air from the leaves. This reduces photosynthesis and the productivity of fruit and forest trees, and disfigures ornamental plants and fruit. Unchecked infestations of the cottony cushion scale can have a severe impact on fruit-growing and horticultural industries, and on the endemic fauna of small islands.
Taxonomic TreeTop of page
- Domain: Eukaryota
- Kingdom: Metazoa
- Phylum: Arthropoda
- Subphylum: Uniramia
- Class: Insecta
- Order: Hemiptera
- Suborder: Sternorrhyncha
- Unknown: Coccoidea
- Family: Monophlebidae
- Genus: Icerya
- Species: Icerya purchasi
Notes on Taxonomy and NomenclatureTop of page
I. purchasi belongs to the scale insect family Monophlebidae, the giant scales. The genus Icerya has been poorly studied and it is possible that there are other species similar to I. purchasi living in the same geographical areas. Rao (1951) reviewed the known species of Icerya living in the Oriental Region, and a revision of the known species in Australia is currently in progress.
DescriptionTop of page Immature I. purchasi have black limbs and an orange-brown body that is coated with white and yellow wax. The adult female I. purchasi are easily recognized by their large size (up to 10 mm long), red-brown body colour and covering of granular, white wax. The legs, antennae and body hairs are conspicuously black. The nymphs and adult females produce long, hair-like, transparent rods of wax from the body. On reaching maturity, the female produces a white, fluted, wax ovisac with a series of uniform ridges running lengthwise over the surface. As the ovisac is produced, the rear end of the body is tilted upwards, sometimes almost perpendicular to the plant surface. The ovisac may reach the same length as the body, giving an overall combined length of up to 20 mm.
The males are rarely encountered and do not live long. The immature male stages are similar in appearance to those of the female. Pupation occurs in a fluffy, oblong white cocoon. The adult male has well developed antennae, one pair of dusky wings, a red body and tufts of long setae at the end of the abdomen.
Precise identification of Icerya species requires specimens to be mounted on microscope slides and to be studied under high magnification. The microscopic features of I. purchasi are described and illustrated by Rao (1951), Howell and Beshear (1981), Williams and Watson (1990) and Morales (1991). I. purchasi is distinctive in possessing two pairs of abdominal spiracles, three cicatrices and body setae that are conspicuously black even after staining.
DistributionTop of page I. purchasi is generally considered to have originated in Australia. It has a wide climatic tolerance and, unlike related Icerya species, has become established as a pest in southern Europe. It is periodically discovered in greenhouses in temperate regions, but is not generally a pest in these situations. The recent discovery of relatively dense infestations in London, UK caused concern initially, but the natural enemy (vedalia beetle, Rodolia cardinalis) has apparently been accidentally introduced also; this appears to have become established in some of the London populations (Salisbury and Booth, 2004).
The distribution map includes records based on specimens of I. purchasi from the collection in the Natural History Museum, London, UK (NHM, various dates).
Distribution TableTop of page
The distribution in this summary table is based on all the information available. When several references are cited, they may give conflicting information on the status. Further details may be available for individual references in the Distribution Table Details section which can be selected by going to Generate Report.
|Continent/Country/Region||Distribution||Last Reported||Origin||First Reported||Invasive||Reference||Notes|
|China||Restricted distribution||EPPO, 2014|
|-Anhui||Present||Introduced||Invasive||CIE, 1971; EPPO, 2014|
|-Fujian||Present||Introduced||Invasive||CIE, 1971; Tao, 1999; EPPO, 2014|
|-Guangdong||Present||Introduced||Invasive||CIE, 1971; Tao, 1999; EPPO, 2014|
|-Guangxi||Present||Introduced||Invasive||CIE, 1971; Tao, 1999; EPPO, 2014|
|-Hebei||Present||Introduced||Invasive||CIE, 1971; Tao, 1999|
|-Hong Kong||Present||Introduced||Invasive||CIE, 1971; Tao, 1999; EPPO, 2014|
|-Hubei||Present||Introduced||Invasive||CIE, 1971; Tao, 1999; EPPO, 2014|
|-Jiangsu||Present||Introduced||Invasive||Tao, 1999; EPPO, 2014|
|-Nei Menggu||Present||Introduced||Invasive||Tao, 1999|
|-Shaanxi||Present||Introduced||Invasive||Fan et al., 1988; Tao, 1999|
|-Shandong||Present||Introduced||Invasive||CIE, 1971; Tao, 1999; EPPO, 2014|
|-Sichuan||Present||Introduced||Invasive||CIE, 1971; EPPO, 2014|
|-Yunnan||Present||Introduced||Invasive||CIE, 1971; Tao, 1999; EPPO, 2014|
|-Zhejiang||Present||Introduced||Invasive||Hua et al., 1999; EPPO, 2014|
|Christmas Island (Indian Ocean)||Present||Introduced||Invasive||CIE, 1971; EPPO, 2014|
|Cocos Islands||Present||Introduced||Invasive||NHM, 1981|
|Georgia (Republic of)||Present||Introduced||Invasive||CIE, 1971; EPPO, 2014|
|India||Restricted distribution||EPPO, 2014|
|-Andhra Pradesh||Present||Introduced||Invasive||CIE, 1971; EPPO, 2014|
|-Kerala||Present||Introduced||Invasive||Rao, 1951; EPPO, 2014|
|-Madhya Pradesh||Present||Meshram and Vijayaraghavan, 2004|
|-Maharashtra||Present||Introduced||Invasive||CIE, 1971; EPPO, 2014|
|-Odisha||Present||Introduced||Invasive||CIE, 1971; EPPO, 2014|
|-Tamil Nadu||Present||Introduced||Invasive||CIE, 1971; EPPO, 2014|
|-Uttar Pradesh||Present||Verma et al., 2012|
|-West Bengal||Present||Introduced||Invasive||Konar, 1998|
|Indonesia||Restricted distribution||EPPO, 2014|
|-Irian Jaya||Present||Introduced||Invasive||CIE, 1971|
|-Java||Present||Introduced||Invasive||CIE, 1971; EPPO, 2014|
|-Sulawesi||Present||Introduced||Invasive||CIE, 1971; EPPO, 2014|
|-Sumatra||Present||Introduced||Invasive||CIE, 1971; EPPO, 2014|
|Iran||Present||Introduced||Invasive||CIE, 1971; EPPO, 2014|
|Iraq||Present||Introduced||Invasive||CIE, 1971; EPPO, 2014|
|Israel||Widespread||Introduced||Invasive||CIE, 1971; EPPO, 2014|
|-Honshu||Present||Introduced||Invasive||CIE, 1971; EPPO, 2014|
|-Kyushu||Present||Introduced||Invasive||CIE, 1971; EPPO, 2014|
|-Ryukyu Archipelago||Present||Introduced||Invasive||CIE, 1971; EPPO, 2014|
|Jordan||Present||Introduced||Invasive||CIE, 1971; EPPO, 2014|
|Korea, DPR||Present||Introduced||Invasive||CIE, 1971|
|Korea, Republic of||Present||Introduced||Invasive||APPPC, 1987; EPPO, 2014|
|Lebanon||Present||Introduced||Invasive||CIE, 1971; EPPO, 2014|
|Malaysia||Present||Introduced||Invasive||CIE, 1971; Waterhouse, 1993; EPPO, 2014|
|-Peninsular Malaysia||Present||Introduced||Invasive||CIE, 1971|
|Maldives||Present||Introduced||Invasive||Watson et al., 1995|
|Pakistan||Present||Introduced||Invasive||CIE, 1971; EPPO, 2014|
|Saudi Arabia||Present||Introduced||Invasive||CIE, 1971; EPPO, 2014|
|Sri Lanka||Present||Introduced||Invasive||CIE, 1971; EPPO, 2014|
|Syria||Present||Introduced||Invasive||CIE, 1971; EPPO, 2014|
|Taiwan||Present||Introduced||Invasive||CIE, 1971; Tao, 1999; Wong et al., 1999; EPPO, 2014|
|Turkey||Present||Introduced||Invasive||CIE, 1971; EPPO, 2014|
|Vietnam||Present||Introduced||Invasive||CIE, 1971; Waterhouse, 1993; EPPO, 2014|
|Algeria||Present||Introduced||Invasive||CIE, 1971; EPPO, 2014|
|Angola||Present||Introduced||Invasive||CIE, 1971; EPPO, 2014|
|Cape Verde||Present||Introduced||Invasive||CIE, 1971; EPPO, 2014|
|Congo Democratic Republic||Present||EPPO, 2014|
|Egypt||Present||Introduced||Invasive||CIE, 1971; EPPO, 2014|
|Ethiopia||Present||Introduced||Invasive||CIE, 1971; Getu, 1996; EPPO, 2014|
|Kenya||Present||Introduced||Invasive||CIE, 1971; EPPO, 2014|
|Libya||Present||Introduced||Invasive||CIE, 1971; EPPO, 2014|
|Madagascar||Present||Introduced||Invasive||CIE, 1971; EPPO, 2014|
|Malawi||Present||Introduced||Invasive||CIE, 1971; EPPO, 2014|
|Mauritius||Present||Introduced||Invasive||CIE, 1971; EPPO, 2014|
|Morocco||Present||Introduced||Invasive||CIE, 1971; EPPO, 2014|
|Mozambique||Present||Introduced||Invasive||CIE, 1971; EPPO, 2014|
|Saint Helena||Present||Introduced||Invasive||CIE, 1971; EPPO, 2014|
|Sao Tome and Principe||Present||Introduced||Invasive||CIE, 1971; EPPO, 2014|
|Senegal||Present||Introduced||Invasive||CIE, 1971; EPPO, 2014|
|Seychelles||Present||Introduced||Invasive||CIE, 1971; EPPO, 2014|
|Somalia||Present||Introduced||Invasive||CIE, 1971; EPPO, 2014|
|South Africa||Present||Introduced||Invasive||CIE, 1971; EPPO, 2014|
|-Canary Islands||Present||Introduced||Invasive||CIE, 1971; EPPO, 2014|
|Sudan||Present||Introduced||Invasive||CIE, 1971; EPPO, 2014|
|Tanzania||Present||Introduced||Invasive||CIE, 1971; EPPO, 2014|
|Togo||Present||Introduced||Invasive||CIE, 1971; EPPO, 2014|
|Tunisia||Present||Introduced||Invasive||CIE, 1971; EPPO, 2014|
|Uganda||Present||Introduced||Invasive||CIE, 1971; EPPO, 2014|
|Zambia||Present||Introduced||Invasive||CIE, 1971; EPPO, 2014|
|Zimbabwe||Present||Introduced||Invasive||CIE, 1971; EPPO, 2014|
|Bermuda||Present||Introduced||Invasive||CIE, 1971; EPPO, 2014|
|Mexico||Present||Introduced||Invasive||CIE, 1971; EPPO, 2014|
|USA||Restricted distribution||EPPO, 2014|
|-Alabama||Present||Introduced||Invasive||CIE, 1971; EPPO, 2014|
|-Arizona||Present||Introduced||Invasive||CIE, 1971; EPPO, 2014|
|-California||Present||Introduced||ca 1868||Invasive||CIE, 1971; Gill, 1993; EPPO, 2014|
|-Florida||Present||Introduced||Invasive||CIE, 1971; EPPO, 2014|
|-Georgia||Present||Introduced||Invasive||CIE, 1971; EPPO, 2014|
|-Hawaii||Present||Introduced||pre-1890||Invasive||CIE, 1971; EPPO, 2014|
|-Louisiana||Present||Introduced||Invasive||CIE, 1971; EPPO, 2014|
|-Mississippi||Present||Introduced||Invasive||CIE, 1971; EPPO, 2014|
|-Montana||Present||Introduced||Invasive||CIE, 1971; EPPO, 2014|
|-New Mexico||Present||Introduced||Invasive||CIE, 1971; EPPO, 2014|
|-North Carolina||Present||Introduced||Invasive||CIE, 1971; EPPO, 2014|
|-Oklahoma||Present||Introduced||Invasive||CIE, 1971; EPPO, 2014|
|-South Carolina||Present||Introduced||Invasive||CIE, 1971; EPPO, 2014|
|-Texas||Present||Introduced||Invasive||CIE, 1971; EPPO, 2014|
|-Virginia||Present||Introduced||Invasive||CIE, 1971; EPPO, 2014|
Central America and Caribbean
|Antigua and Barbuda||Present||Introduced||Invasive||CIE, 1971; EPPO, 2014|
|Bahamas||Present||Introduced||Invasive||CIE, 1971; EPPO, 2014|
|Barbados||Present||Introduced||Invasive||CIE, 1971; Bennett and Alam, 1985; EPPO, 2014|
|Cayman Islands||Present||Introduced||Invasive||NHM, 1970|
|Cuba||Present||Introduced||Invasive||CIE, 1971; EPPO, 2014|
|Dominican Republic||Present||Introduced||Invasive||CIE, 1971; EPPO, 2014|
|El Salvador||Present||Introduced||Invasive||CIE, 1971; EPPO, 2014|
|Guadeloupe||Present||Introduced||Invasive||CIE, 1971; EPPO, 2014|
|Guatemala||Present||Introduced||Invasive||CIE, 1971; EPPO, 2014|
|Haiti||Present||Introduced||Invasive||NHM, 1972; NHM, 1973|
|Martinique||Present||Introduced||Invasive||CIE, 1971; EPPO, 2014|
|Montserrat||Present||Introduced||Invasive||CIE, 1971; EPPO, 2014|
|Puerto Rico||Present||Introduced||Invasive||CIE, 1971; EPPO, 2014|
|Saint Kitts and Nevis||Present||Introduced||Invasive||NHM, 1971; EPPO, 2014|
|Saint Lucia||Present||Introduced||Invasive||CIE, 1971; EPPO, 2014|
|Trinidad and Tobago||Present||Introduced||Invasive||CIE, 1971; EPPO, 2014|
|Argentina||Present||Introduced||Invasive||CIE, 1971; EPPO, 2014|
|Bolivia||Present||Introduced||Invasive||CIE, 1971; EPPO, 2014|
|-Espirito Santo||Present||Culik et al., 2007; EPPO, 2014|
|-Minas Gerais||Present||Introduced||Invasive||CIE, 1971|
|-Rio de Janeiro||Present||Introduced||Invasive||CIE, 1971|
|-Rio Grande do Sul||Present||Introduced||Invasive||CIE, 1971|
|-Santa Catarina||Present||Introduced||Invasive||CIE, 1971|
|-Sao Paulo||Present||Introduced||Invasive||CIE, 1971|
|Chile||Present||Introduced||Invasive||CIE, 1971; EPPO, 2014|
|Colombia||Present||Introduced||Invasive||CIE, 1971; EPPO, 2014|
|Ecuador||Present||Introduced||Invasive||CIE, 1971; EPPO, 2014|
|-Galapagos Islands||Present||Introduced||Invasive||Peck et al., 1998|
|Guyana||Present||Introduced||Invasive||NHM, 1979; NHM, 1995|
|Paraguay||Present||Introduced||Invasive||CIE, 1971; EPPO, 2014|
|Peru||Present||Introduced||Invasive||CIE, 1971; EPPO, 2014|
|Uruguay||Present||Introduced||Invasive||CIE, 1971; EPPO, 2014|
|Venezuela||Present||Introduced||Invasive||CIE, 1971; EPPO, 2014|
|Albania||Present||Introduced||Invasive||CIE, 1971; EPPO, 2014|
|Cyprus||Widespread||Introduced||Invasive||CIE, 1971; EPPO, 2014|
|France||Restricted distribution||Introduced||Invasive||CIE, 1971; Matile-Ferrero et al., 1999; EPPO, 2014|
|-Corsica||Present||Introduced||Invasive||CIE, 1971; Foldi, 2003; EPPO, 2014|
|Gibraltar||Present||Introduced||Invasive||CIE, 1971; EPPO, 2014|
|Greece||Present||Introduced||Invasive||CIE, 1971; Papadopoulou and Chryssohoides, 2012; EPPO, 2014|
|Italy||Present||Introduced||Invasive||CIE, 1971; EPPO, 2014|
|-Sicily||Present||Introduced||Invasive||Russo et al., 2003; EPPO, 2014|
|Malta||Present||Introduced||Invasive||CIE, 1971; EPPO, 2014|
|Portugal||Present||Introduced||Invasive||CIE, 1971; EPPO, 2014|
|-Azores||Present||Introduced||Invasive||CIE, 1971; EPPO, 2014|
|-Madeira||Present||Introduced||Invasive||CIE, 1971; EPPO, 2014|
|Romania||Present||Introduced||Invasive||CIE, 1971; EPPO, 2014|
|Russian Federation||Present||Introduced||Invasive||CIE, 1971; EPPO, 2014|
|Slovakia||Present||Kollár et al., 2016|
|Spain||Present||Introduced||Invasive||CIE, 1971; Getu, 1996; EPPO, 2014|
|Switzerland||Present||Introduced||Invasive||CIE, 1971; EPPO, 2014|
|UK||Present||Watson and Malumphy, 2004; Malumphy, 2013|
|Yugoslavia (Serbia and Montenegro)||Present||Introduced||Invasive||CIE, 1971|
|Australia||Restricted distribution||EPPO, 2014|
|-Lord Howe Is.||Present||Williams and Watson, 1990|
|-New South Wales||Present||Native||Not invasive||CIE, 1971; EPPO, 2014|
|-Queensland||Present||Native||Not invasive||CIE, 1971; EPPO, 2014|
|-South Australia||Present||Native||Not invasive||CIE, 1971; EPPO, 2014|
|-Tasmania||Present||CIE, 1971; EPPO, 2014|
|-Victoria||Present||Native||Not invasive||CIE, 1971; EPPO, 2014|
|Fiji||Present||Introduced||Invasive||CIE, 1971; Williams and Watson, 1990; EPPO, 2014|
|French Polynesia||Present||Introduced||Invasive||CIE, 1971; Williams and Watson, 1990; EPPO, 2014|
|Guam||Present||Introduced||Invasive||CIE, 1971; EPPO, 2014|
|Marshall Islands||Present||Introduced||Invasive||CIE, 1971; EPPO, 2014|
|Micronesia, Federated states of||Present||Introduced||Invasive||CIE, 1971; EPPO, 2014|
|New Caledonia||Present||Introduced||Invasive||CIE, 1971; EPPO, 2014|
|New Zealand||Present||Introduced||Invasive||CIE, 1971; EPPO, 2014|
|Norfolk Island||Present||Introduced||Invasive||CIE, 1971; Williams and Watson, 1990; EPPO, 2014|
|Northern Mariana Islands||Present||EPPO, 2014|
|Papua New Guinea||Present||CIE, 1971; Williams and Watson, 1990; EPPO, 2014|
|Solomon Islands||Present||Introduced||Invasive||CIE, 1971; Williams and Watson, 1990; EPPO, 2014|
|Tonga||Present||Introduced||Invasive||CIE, 1971; Williams and Watson, 1990; EPPO, 2014|
|US Minor Outlying Islands||Present||EPPO, 2014|
History of Introduction and SpreadTop of page I. purchasi is native to Australia; it was accidentally introduced to California in about 1868 and devastated the citrus industry there until a natural enemy from Australia was introduced in 1888. This was the first ever example of successful classical biological control. The pest also reached New Zealand and South Africa at about the same time, and has subsequently spread widely through most of the tropical and subtropical countries of the world (Bartlett, 1978). Recently it has begun to extend its range northwards, being recorded for the first time breeding outdoors in Paris, France in 2000 (Matile-Ferrero et al., 1999) and in London, UK in 2002 (G Watson, [address available from CABI], personal communication, 2004); this may be due to climate warming (G Watson, [address available from CABI], personal communication, 2004).
Risk of IntroductionTop of page I. purchasi is widespread throughout the tropical and warmer temperate regions. It is probable that it occurs in more countries than are indicated by the distribution map, and it would easily establish in any remaining areas that have appropriate climatic conditions.
Accidental introduction to new territories is possible through the movement of infested live plants through shipping or air transport/mail. This insect moves between countries on live plant material, particularly in shipments of whole ornamental plants and fruit trees.
Hosts/Species AffectedTop of page The list of hosts is not exhaustive. I. purchasi lives on a wide variety of hosts, especially woody plants.
Growth StagesTop of page Flowering stage, Fruiting stage, Vegetative growing stage
SymptomsTop of page Sap depletion may lead to wilting, leaf drop, dieback, and stunted growth. As with most sap-sucking insects, the production of honeydew leads to the growth of sooty mould.
List of Symptoms/SignsTop of page
|Growing point / dieback|
|Leaves / abnormal leaf fall|
|Leaves / honeydew or sooty mould|
|Leaves / honeydew or sooty mould|
|Stems / external feeding|
|Stems / honeydew or sooty mould|
|Whole plant / dwarfing|
Biology and EcologyTop of page I. purchasi have four ('female') or five (male) developmental stages. As with all scale insects, the females do not produce wings and look similar to the immature stages. The males possess a single pair of dusky wings. However the 'females' are actually hermaphrodites with fertilization occurring between the eggs and the sperm of the same individual. Sexually functional males are occasionally produced from unfertilized eggs, but mating is not necessary for reproduction (Morales, 1992).
The adult females produce 500 to 2000 bright-red, oblong eggs over a period of 2 to 3 months. The number of eggs produced depends on the body size, condition of the host and climatic conditions. After leaving the egg sac, the crawlers settle along the midribs and veins of the leaves. The next two instars migrate to the larger twigs and branches and eventually moult into the adult 'female' (Morales, 1992). There are two to four generations per year. Cottony cushion scale infestations are often attended by ants that are attracted to the sugary honeydew excreted by the scales (Getu, 1996).
Natural enemiesTop of page
|Natural enemy||Type||Life stages||Specificity||References||Biological control in||Biological control on|
|Cryptochetum iceryae||Parasite||Nymphs||Bermuda;Chile;Egypt;India;Israel;New Zealand;Peru;Sao Tome and Principe;South Australia;St Kitts Nevis;USA||Acacia baileyana; Acalypha; Citrus; Erythrina umbrosus; fruit trees; ornamental plants; roses; Tamarix|
|Rodolia cardinalis||Predator||Adults/Eggs/Nymphs||Antigua; Ascension; Australia; South Australia; Bahamas; Barbados; Bermuda; California; Cayman Islands; Chile; Cyprus; Ecuador; Egypt; Ethiopia; France; Greece; Guam; Hawaii; Hong Kong; Israel; Italy; Kenya; Madagascar; Malta; Montserrat; New Zealand; Peru; Philippines; Portugal; Puerto Rico; Republic of Georgia; Sao Tome and Principe; Senegal; South Africa; Spain; Sri Lanka; St Helena; St Kitts Nevis; Switzerland; Taiwan; Uruguay; USA; USSR; Venezuela; Yugoslavia||Acacia; Acacia baileyana; Acalypha; Casuarina; Citrus; fruit trees; orchards; ornamental plants; pigeon peas; roses; Tamarix|
|Rodolia koebelei||Predator||Adults/Eggs/Nymphs||Hawaii; USA||Citrus|
Notes on Natural EnemiesTop of page Most of the recorded distributions of the natural enemies of I. purchasi are species introduced from other geographical areas for its control. The origin of I. purchasi is generally considered to be Australia, and other natural enemies are likely to occur in its natural habitat.
Means of Movement and DispersalTop of page Natural Dispersal (Non-Biotic Factors)
The dispersal stage of the giant mealybugs is the first-instar crawler stage (G Watson, [address available from CABI], personal communication, 2004); these are often dispersed passively in the wind, and have been recorded being taken by the wind to an altitude of 6 metres and a distance of 3.5 kilometres (Hill, 1980).
The crawlers may also be carried passively by animals and people that come into contact with the host plant.
Harvesting infested plant material, e.g. fruit, aids dispersal by scattering the crawlers into the air, where the wind may carry them away. Prunings of infested plants, and the clothing, tools and vehicles of agricultural workers, can become contaminated with the crawlers and so aid in their dispersal.
Plant TradeTop of page
|Plant parts liable to carry the pest in trade/transport||Pest stages||Borne internally||Borne externally||Visibility of pest or symptoms|
|Bark||larvae||Yes||Pest or symptoms usually visible to the naked eye|
|Flowers/Inflorescences/Cones/Calyx||adults; eggs; larvae; nymphs; pupae||Yes||Pest or symptoms usually visible to the naked eye|
|Fruits (inc. pods)||adults; eggs; larvae; nymphs; pupae||Yes||Pest or symptoms usually visible to the naked eye|
|Leaves||adults; eggs; larvae; nymphs; pupae||Yes||Pest or symptoms usually visible to the naked eye|
|Seedlings/Micropropagated plants||adults; eggs; larvae; nymphs; pupae||Yes||Pest or symptoms usually visible to the naked eye|
|Stems (above ground)/Shoots/Trunks/Branches||adults; eggs; larvae; nymphs; pupae||Yes||Pest or symptoms usually visible to the naked eye|
|Plant parts not known to carry the pest in trade/transport|
|Growing medium accompanying plants|
|True seeds (inc. grain)|
Wood PackagingTop of page
|Wood Packaging liable to carry the pest in trade/transport||Timber type||Used as packing|
|Solid wood packing material with bark||No|
|Wood Packaging not known to carry the pest in trade/transport|
|Loose wood packing material|
|Processed or treated wood|
|Solid wood packing material without bark|
Impact SummaryTop of page
|Fisheries / aquaculture||None|
ImpactTop of page Damage to the plant by I. purchasi is mostly caused by sap depletion; the shoots dry up and die, and defoliation occurs. In addition, the copious quantities of honeydew produced by the scales coat the leaves, blocking the stomata and impeding gas exchange. Such fouling frequently results in the growth of sooty moulds over the leaf surfaces, which blocks light from the mesophyll, so reducing photosynthesis.
I. purchasi is a particular pest of citrus, Acacia spp., Casuarina spp. and Pittosporum spp., but it can damage many types of fruit and forest trees, and ornamental shrubs and trees. After its introduction into California, USA, in the late nineteenth century, it was recorded devastating citrus orchards, killing even large trees. By 1887, the problem on citrus had increased to such serious proportions that the entire citrus industry of California was threatened with destruction (Bartlett, 1978). Serious damage to citrus orchards by I. purchasi was also recorded in many other countries when the cottony cushion scale first arrived (Williams and Watson, 1990), but with successful biological control this insect has become relatively unimportant in fruit orchards today.
In Anhui, China, I. purchasi is one of the most important pests of pomegranates (Punica granatum) (Wang et al., 2002), and in Zhejiang, China, the cottony cushion scale is the main pest damaging Liquidambar formosana (Formosan-gum) (Hua et al., 1999). In Israel, the cottony cushion scale was a serious pest in the northern part of the country until biological control became established, which reduced it to minor pest status (Ben-Dov, 1995).
Impact: BiodiversityTop of page The relatively recent establishment of I. purchasi in the Galapagos Islands (Peck et al., 1998) has caused concern because the pest has attacked a wide range of plants, including some of the endemic flora, and could endanger the native flora and the fauna dependant on it (Roque-Albelo, 2003). A biological control programme is currently underway (Causton, 2003).
Detection and InspectionTop of page I. purchasi is usually found along major veins on the lower surfaces of the leaves, and on the stems of host plants. It congregates in large masses and is very conspicuous. Long-established infestations are often surrounded by sooty mould growth, and may be attended by ants.
Similarities to Other Species/ConditionsTop of page I. purchasi is most similar to the Seychelles scale, Icerya seychellarum, but differs by having granular white wax covering the body, whereas I. seychellarum has tufts of yellow wax along the dorsum and around the margins; and in lacking conspicuous black body hairs. In addition, the ovisac of I. purchasi is large and fluted, whereas that of I. seychellarum is smaller, and fluffy rather than fluted. I. seychellarum does not congregate in masses.
Slide-mounted specimens of I. purchasi can be distinguished from the other common species of Icerya by the presence of two pairs of abdominal spiracles, three cicatrices and black body hairs.
Prevention and ControlTop of page
Due to the variable regulations around (de)registration of pesticides, your national list of registered pesticides or relevant authority should be consulted to determine which products are legally allowed for use in your country when considering chemical control. Pesticides should always be used in a lawful manner, consistent with the product's label.
All life stages of I. purchasi are covered with wax, which reduces the effectiveness of most chemical insecticides. In addition, the use of insecticides prevents regulation by natural enemies, which has proved to be highly successful with this species. In the Spanish citrus industry, it is important to only use pesticides when absolutely necessary to ensure that the biological control agents of the citrus pests are not significantly injured; side-effect testing of pesticides on the control agents has been routinely carried out in Spain for many years (Jacas Miret and Garcia Mari, 2001).
The insect growth regulator pyriproxyfen has been found to be as effective in controlling I. purchasi (Gokkes et al., 1989). Good control was achieved when applied alone or with 0.5% mineral oil (Peleg, 1989). Another growth regulator, buprofezin, gave 100% mortality of crawlers and 31% decreased egg hatch when the adults were sprayed with it (Mendel et al., 1991).
In Italy, trials on the effect of azadirachtin A (extracted from neem) on the development and fecundity of Rodolia cardinalis indicated that use of this organic insecticide can adversely affect biological control of the cottony cushion scale (Heimbach, 2002).
The regulation of I. purchasi by natural enemies is one of the classic success stories in biological control. When I. purchasi established in California, USA in 1868/1869, it was apparent that it could be a major impediment to citrus production. In 1888, the United States Department of Agriculture (USDA) imported various natural enemies from Australia, including the vedalia beetle, Rodolia cardinalis. Vedalia immediately proved highly effective in controlling I. purchasi and has subsequently been distributed to about 57 countries (Bartlett, 1978). It has continued to be effective in controlling I. purchasi, except in areas where the indiscriminate use of insecticides has killed the predator. In areas with extreme winters, which kill off the vedalia populations, periodic re-introduction has been necessary.
I. purchasi living on plants such as Spartium junceum, which contain alkaloids, are not completely controlled by R. cardinalis. Caltagirone and Doutt (1989) suggested that these plants (with residual populations of the scale) provide permanent sources of vedalia that will disperse into new infestations of scale on citrus and bring them under control.
A detailed history of the introduction of the vedalia beetle into California, USA, is given by Caltagirone and Doutt (1989).
The parasitoid Cryptochaetum iceryae has also proved to be effective in regulating I. purchasi populations. Adult C. iceryae are sensitive to heat and aridity and are most effective in regulating cottony cushion scale populations in cooler coastal areas. In more arid and hot inland areas, vedalia beetles are more effective. Studies in inland California (Quezada and DeBach, 1973) have shown that the two natural enemies seasonally share their prey in different proportions and are fairly even in their competitive abilities, Rodolia usually taking more prey during summer and autumn and Cryptochaetum taking more during winter and early spring. Competition between the two natural enemies did not increase host survival and these studies provide strong support for the importation of multiple natural enemies.
Various other natural enemies have been tried against I. purchasi, but with little success.
Careful management is necessary when using pesticides against other pests if biological control of I. purchasi is in operation, because damage to the populations of biocontrol agent can cause an outbreak of I. purchasi, as recorded in South Africa by Hattingh and Tate (1995).
Ants attending I. purchasi infestations to collect the sugary honeydew excreted (Getu, 1996), may defend the scales from attack by their natural enemies, so making the pest problem worse. If large numbers of ants attend a heavy infestation of the scale, it may be worthwhile controlling the ants to help the natural enemies bring the scale population under control quickly.
ReferencesTop of page
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Distribution MapsTop of page
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