Icerya purchasi Maskell, 1879
Cottony cushion scale, Australian bug, Australian fluted scale, Citrus fluted scale, Fluted scale, Mealy scale, White scale
Pericerya purchasi Silvestri, 1939
Since Clare Morales revision of New Zealand Margarodidae in 1991, there has been a revision of the family classification that affects the genera found in New Zealand. Cottony cushion scale, Icerya purchase is now in the family Monophlebidae.
Biostatus and distribution
This adventive scale insect from Australia was first found in New Zealand in 1877 after which it became a serious pest on trees and shrubs, including citrus orchards, until controlled by the Australian cardinal ladybird, Rodolia cardinalis (Coccinellidae) and the fly, Cottony cushion scale parasitoid, Cryptochaetum iceryae (Cryptochetidae). The Cottony cushion scale has spread to many countries throughout the world. In New Zealand it is occasionally found in gardens, parks and native habitats in both North and South islands.
Conservation status: An Australian scale insect occasionally found in gardens, parks and native habitats in both North and South islands.
Life stages and annual cycle
There are two generations a year in New Zealand, though most life stages may be found in most months of the year. Many of the following details come from Clare Morales 1991 paper on the Margarodidae. This scale insect has two methods of reproduction, normal bisexual reproduction and Gynomonoecious where the hermaphrodite adult 'female' contains an ovotestis and fertilisation occurs between eggs and sperm in the same adult. The testes develops first. The occasional unfertilised egg develops into an adult winged male.
The Cottony cushion scale has four ('female') or five (male) developmental stages. The body of the adult ‘female’ is up to 10 mm long, pale to dark brown and covered in white or pale yellowish wax, with long black hairs and setae. It has one pair of black antennae and three pairs of black legs. On the underside of the head is a short rostrum that hold the stylets used for feeding. 'Females' laying eggs produce a long, white, fluted egg sac. It may contain 500-1000 bright red, oblong eggs. The eggs hatch into first instar (stage) nymphs that have pale red-brown bodies and like the adult ‘female’ three pairs of black legs and black antennae. The body is covered with a little white wax and long, glassy body setae (hairs). They squeeze out between the 'flutes' in the egg sac and settle along the mid rib and veins of the host plant leaves. Like the adult 'female' they have a ventral rostrum that holds the stylets used for feeding. When fully grown, the nymph moults into the next nymphal stage. The second and third instars are reddish-brown and covered with tufts of glassy setae, black hairs and yellow and white wax. They tend to migrate to larger twigs and branches.
Adult males are uncommon and do not live long. They have one pair of dusky wings. At the end of their abdomen they have fleshy lobes bearing tufts of long setae. Male nymphs are similar in appearance to those of the female. The last male nymph makes a fluffy oblong white cocoon in which it pupates.
Nymphs and adult females of Cottony cushion scale have sucking mouthparts. Specially shaped long rods called stylets are used for feeding. Until used for feeding the tips of the stylets held in the short sheath-like rostrum. When it wishes to feed, the scale insect moves the tip of the rostrum onto the surface of the plant. The stylets are then gradually pushed into the plant. The stylets form two tubes, one down which saliva is pumped into plant cells and the second tube through which it sucks the contents of the plant cells. If the insect inserts its stylets into the phloem, the plant vessels for transmitting sap from the leaves to other parts of the plant. The sap has a high volume of water and sugars, more than the insect needs. It excretes the excess water and sugar, which is called honeydew.
Walking, flying and dispersal
The nymphs, adult females and males have legs large enough for walking. All these stages can walk around the leaves and stems of the plant on which they are born. The main stage that spreads to new host plants is probably the first instar (stage) nymph. In other insects this stage can be disperse long distances by air. It is not known if crawlers of this species go to high points of the plant and stand up to catch the wind.
Adult males have wings as well as legs. They can walk over leaves and stems in search of females with which to mate. They can also fly to other parts of the tree or nearby colonies, and may be carried further by wind.
Scale insects in the family Monophlebidae require specialist skills for their identification, but the only species in New Zealand, the Cottony cushion scale, is sufficiently distinctive to enable its identification on its host plants.
Adult females are large, up to 10 mm long, and have a red-brown body covered with white granular wax. When mature, they make a white, fluted, egg sac. As it enlarges the female body is tilted upwards. The nymphs have an orange brown body that is coated with white and yellow wax.
No pathogens of Cottony cushion scale are known in New Zealand.
Five parasitoids are present in New Zealand. Four are wasp and one is a fly. The fly, Cottony cushion scale parasitoid, Cryptochaetum iceryae, is from Australia and was first sent to New Zealand in 1888.
Two of the wasps are hypoparasites, that is they parasitise other parasites. One, Euryischia sp. (Aphelinidae) is a parasite of the parasitic fly. The other, Coccidoctonus dubius (Encyrtidae) is a parasite of parasitic wasps.
Three of the four predators of the Cottony cushion scale in New Zealand are ladybirds. One of which is the famous Vedalia beetle or Cardinal ladybird, Rodolia cardinalis. The use of this Australian ladybird to control Cottony cushion scale in California was an early example of successful biological control.
The larvae of one of the wasp parasitoids sometimes behaves like a predator by feeding on the eggs of the scale insect.
|Scientific Name||Common Name||Classification||Enemy Type||Reliability Index||Biostatus|
|Coccidoctonus dubius (Girault, 1915)||(Wasp)||Hymenoptera: Encyrtidae||parasitoid||10||adventive|
|Cryptochaetum iceryae (Williston, 1888)||Cottony cushion scale parasitoid (Fly)||Diptera: Cryptochetidae||parasitoid||10||adventive|
|Euryischia sp.||(Wasp)||Hymenoptera: Aphelinidae||parasitoid||8||unknown|
|Ophelosia crawfordi Riley, 1890||(Wasp)||Hymenoptera: Pteromalidae||parasitoid||10||adventive|
|Tetracnemoidea brevicornis (Girault, 1915)||(Wasp)||Hymenoptera: Encyrtidae||parasitoid||10||adventive|
|Coccinella undecimpunctata Linnaeus, 1758||Eleven-spotted ladybird (Beetle)||Coleoptera: Coccinellidae||predator||10||adventive|
|Ophelosia crawfordi Riley, 1890||(Wasp)||Hymenoptera: Pteromalidae||predator||10||adventive|
|Rodolia cardinalis (Mulsant, 1850)||Cardinal ladybird (Beetle)||Coleoptera: Coccinellidae||predator||10||adventive|
|Rodolia koebelei (Coquillett, 1893)||Koebele's ladybird (Beetle)||Coleoptera: Coccinellidae||predator||10||adventive|
Cottony cushion scale is found on cultivated, naturalised and native plants. It is rarely a pest because numbers are kept low though biological control. The nymphs are mainly found on leaves while the egg laying females are mostly seen on stems.
Feeding and honeydew
Like other Hemiptera, the adult female and nymphs of Cottony cushion scale have sucking mouth parts. The long stylets, special shaped rods, are held in a short rostrum on the underside of the body. When the insect wishes to feed the stylets are then gradually pushed into the plant. The inner pair of stylets, form two tubes, one through which saliva is injected into the plant and a second through which plants juices are sucked up into the insect. The adult female and nymphs of Cottony cushion scale may insert their stylets into the phloem, the plant vessels for transmitting sap from the leaves to other parts of the plant. The sap has a high volume of water and sugars, more than the insect needs. It excretes the excess water and sugar, which is called honeydew. Sooty moulds may grow on the honeydew.
|Common Name(s)||Scientific Name||Family||Reliability Index||Biostatus|
|Bailey's wattle, Cootamundra wattle, Golden wattle||Acacia baileyana F. Muell.||Leguminosae||10||naturalised|
|Bower Wattle, Narrow-leaf Bower Wattle, River Wattle||Acacia cognata Domin||Leguminosae||10||cultivated|
|Mimosa, Silver Wattle, Sydney Black Wattle||Acacia dealbata Link||Leguminosae||10||naturalised|
|Gossamer wattle, Sally wattle, White sallow wattle||Acacia floribunda (Vent.) Willd.||Leguminosae||10||naturalised|
|Kangaroo acacia||Acacia ornata||Leguminosae||10||cultivated|
|Chinese gooseberry, Kiwifruit, Yang-tao||Actinidia deliciosa (A.Chev.) C.F.Liang & A.R.Ferguson||Actinidiaceae||10||naturalised|
|North Island broom, Mākaka, Maukoro, Tainoka, Tawao, Maukoro||Carmichaelia australis R.Br.||Leguminosae||10||endemic|
|Meyer lemon, Chinese dwarf lemon||Citrus ×meyeri Yu. Tanaka||Rutaceae||10||cultivated|
|Kākawariki, Kanono, Kapukiore, Karamū-kueo, Kueo (fruit), Manono, Pāpāuma, Raurēkau, Toherāoa||Coprosma grandifolia Hook.f.||Rubiaceae||10||endemic|
|Coastal Coprosma, Taupata||Coprosma repens A.Rich.||Rubiaceae||10||endemic|
|Broad-leaved fleabane, Tall fleabane, Hāka, Kaingarua, Porerarua, Pouhawaiki||Erigeron sumatrensis Retz.||Compositae||10||naturalised|
|Fatsia, Glossy-leaved paper plant, Japanese aralia, Rice paper plant, Yatsude||Fatsia japonica (Thunb.) Decne. & Planch.||Araliaceae||10||naturalised|
|Big mountain palm, Umbrella palm||Hedyscepe canterburyana (C.Moore & F.Muell.) H.Wendl. & Drude||Palmae||10||cultivated|
|Bay, Laurel, Sweet bay||Laurus nobilis L.||Lauraceae||10||naturalised|
|Apple, Crab-apple||Malus sp.||Rosaceae||7||unknown|
|Poataniwha, Tātaka||Melicope simplex A.Cunn.||Rutaceae||10||endemic|
|Houkūmara, Koheriki, Tākaka, Tātaka, Wharangi, Wharangipiro||Melicope ternata J.R.Forst. & G.Forst.||Rutaceae||10||endemic|
|Scrub pohuehue, Small-leaved pohuehue, Wire vine, Pōhue, Pōhuehue, Pōpōhue, Tororaro, Waekāhu||Muehlenbeckia complexa (A.Cunn.) Meissn.||Polygonaceae||9||indigenous, non-endemic|
|Ngaio||Myoporum laetum G.Forst.||Scrophulariaceae||10||endemic|
|Red mapou, Red matipo, Māpau, Māpou, Mataira, Matipou, Takapou, Tāpau, Tīpau||Myrsine australis (A.Rich.) Allan||Primulaceae||9||endemic|
|Akepiro, Kūmara-kai-torouka, Tanguru, Wharangi-piro||Olearia furfuracea (A.Rich.) Hook.f.||Compositae||10||endemic|
|Coastal tree daisy||Olearia solandri (Hook.f.) Hook.f.||Compositae||10||endemic|
|Pittosporum bracteolatum Endl.||Pittosporaceae||10||cultivated|
|Kaikaro, Karo, Kīhihi||Pittosporum crassifolium Banks & Sol. ex A.Cunn.||Pittosporaceae||10||endemic|
|Pittosporum ellipticum Kirk||Pittosporaceae||10||endemic|
|Lemonwood, Kīhihi, Tarata||Pittosporum eugenioides A.Cunn.||Pittosporaceae||10||endemic|
|Black matipo, Kaikaro, Kōhūhū, Kohukohu, Koihu, Kōwhiwhi, Māpauriki, Pōhiri, Pōwhiri, Rautāwhiri, Tāwhiri||Pittosporum tenuifolium Sol. ex Gaertn.||Pittosporaceae||10||endemic|
|Coastal kowhai||Sophora chathamica Cockayne||Leguminosae||10||endemic|
|Large-leaved kowhai, North Island kowhai, Kōwhai||Sophora tetraptera J.S. Miller||Leguminosae||10||endemic|
|Milk tree, Small-leaved milk tree, Turepo, Ewekuri, Tāwari, Tūrepo||Streblus heterophyllus (Blume) Corner||Moraceae||10||endemic|
|Gorse||Ulex europaeus L.||Leguminosae||10||naturalised|
|Furze, Gorse, Whin||Ulex sp.||Leguminosae||7||naturalised|
|Tree nettle, Ongaonga, Taraonga, Taraongaonga||Urtica ferox G.Forst.||Urticaceae||10||endemic|
|Hebe||Veronica stricta Banks & Sol. ex Benth. var. stricta||Plantaginaceae||10||endemic|
|New Zealand oak, Kauere, Pūriri||Vitex lucens Kirk||Labiatae||10||endemic|
Biological control of pests
Biological control of aphids and other herbivorous pests can reduce the impact of the pests and the need to use insecticides. The cardinal ladybird is an important predator of the Cottony cushion scale, Icerya purchase Maskell, 1879 (Hemiptera: Monophlebidae), which if uncontrolled is a serious pest of citrus trees. The scale insect also infests native and other trees. Both the ladybird and the scale insect are natives of Australia.
The ladybird arrived accidentally in New Zealand and was first reported in 1889. Later more ladybirds were imported from Australia. They were also redistributed around the country to help control the scale insect. The cardinal ladybird has been sent to many parts of the world where it contributes to the successful biological control of cottony cushion scale. Many of the ladybirds sent to California in the 1880s were from Napier, New Zealand and not Australia as is often recorded in texts on Biological Control.
The first attempt at biological control of Cottony cushion scale in New Zealand was the shipment of the fly, Cottony cushion scale parasitoid, Cryptochaetum iceryae, from Australia in 1888. However, information about its establishment was lost and confused, probably because it is less dramatic than the Cardinal ladybird. It provides good bioloical control of Cottony cushion scale in some countries.
In New Zealand, natural enemies of cottony cushion scale prevent this insect being a serious pest.
Berry, J.A. 1990: Two parasitoid complexes: Hierodoris atychioides (Butler) (Lepidoptera: Oecophoridae) and Icerya purchasi Maskell (Homoptera: Margarodidae). New Zealand entomologist, 13: 60-62.
CABI Invasive Species Compendium: Icerya purchasi (cottony cushion scale). www.cabi.org/isc/datasheet/28432 (Accessed 23 March 2018).
Morales CF, Bain J 1989. Icerya purchasi Maskell, cottony cushion scale (Homoptera: Margarodidae). In: Cameron PJ, Hill RL, Bain J, Thomas WP ed. A Review of Biological Control of Invertebrate Pests and Weeds in New Zealand 1847 to 1987. Technical Communication No. 10. Wallingford, Oxon, UK, CAB International. Pp. 207-211.
Morales CF. 1991. Margarodidae (Insecta: Hemiptera). Fauna of New Zealand. 21: 1-123.
Plant-SyNZ: Invertebrate herbivore-host plant association database. plant-synz.landcareresearch.co.nz/
The New Zealand Institute for Plant & Food Research Limited (Plant & Food Research) for permission to use photographs.
1 December 2018. NA Martin. Changed symbol used for apostrophes.