INTERESTING INSECTS

By N A Martin (2018)

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.

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 cycle of Cottony cushion scale, Icerya purchasi (Hemiptera: Margarodidae). Figure 11. in Morales C.F. 1991. Margarodidae (Insecta: Hemiptera). Fauna of New Zealand. 21. Creator: Clare Morales. © Landcare Research. [Image: 2R0L]

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.

Feeding

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.

An immature adult female Cottony cushion scale, Icerya purchasi (Hemiptera: Monophlebidae) on a stem of Melicope simplex (Rutaceae). Creator: Darren Snaith. © Plant & Food Research. [Image: 2R07]

An immature adult female Cottony cushion scale, Icerya purchasi (Hemiptera: Monophlebidae) on a stem of Veronica stricta (Plantaginaceae). Creator: Tim Holmes. © Plant & Food Research. [Image: 2R0A]

Two images of an immature adult female Cottony cushion scale, Icerya purchasi (Hemiptera: Monophlebidae) on a stem of Veronica stricta (Plantaginaceae). Creator: Tim Holmes. © Plant & Food Research. [Image: 2R09]

Two images of the underside of an immature adult female Cottony cushion scale, Icerya purchasi (Hemiptera: Monophlebidae). Creator: Tim Holmes. © Plant & Food Research. [Image: 2R0B]

An adult female Cottony cushion scale, Icerya purchasi (Hemiptera: Monophlebidae) with a small egg sac on a stem of North Island Broom, Carmichaelia australis (Leguminosae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2R0G]

An adult female Cottony cushion scale, Icerya purchasi (Hemiptera: Monophlebidae) and egg sac on a stem of Karo, Pittosporum crassifolium (Pittosporaceae): note the white wax on the body of the female. Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2R0F]

An adult female Cottony cushion scale, Icerya purchasi (Hemiptera: Monophlebidae) and egg sac on a stem of Large-leaved kowhai, Sophora tetraptera (Leguminosae): note the tiny first instar (stage) nymph at the edge of the egg sac and the white wax covered nymph on the twig. Creator: Tim Holmes. © Plant & Food Research. [Image: 2R0C]

An adult female Cottony cushion scale, Icerya purchasi (Hemiptera: Monophlebidae) and egg sac on a stem of Large-leaved kowhai, Sophora tetraptera (Leguminosae): note the tiny first instar (stage) nymph crawlinbg on the egg sac and the white wax covered nymph on the stem. Creator: Tim Holmes. © Plant & Food Research. [Image: 2R0D]

Two images of a first instar (stage) nymph of Cottony cushion scale, Icerya purchasi (Hemiptera: Monophlebidae) showing the underside (left) and upper side (right) Creator: Tim Holmes. © Plant & Food Research. [Image: 2R0E]

A recently moulted small nymph of Cottony cushion scale, Icerya purchasi (Hemiptera: Monophlebidae) on a leaf. Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2R0J]

A moulted skin of a nymph of Cottony cushion scale, Icerya purchasi (Hemiptera: Monophlebidae) on a leaf. Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2R0H]

Nymphs of Cottony cushion scale, Icerya purchasi (Hemiptera: Monophlebidae) on a leaf of Tree nettle, Urtica ferox (Urticaceae): note the white wax covering two nymphs. Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2R05]

A moulted skin of a nymph of Cottony cushion scale, Icerya purchasi (Hemiptera: Monophlebidae) on a leaf. Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2R0K]

A large nymph or young adult female Cottony cushion scale, Icerya purchasi (Hemiptera: Monophlebidae) on a leaf. Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2R0I]

A large nymph or young adult female Cottony cushion scale, Icerya purchasi (Hemiptera: Monophlebidae) on a stem of Lemonwood, Pittosporum eugenioides (Pittosporaceae). Creator: Nicholas A. Martin. © Nicholas A. Martin. [Image: 2R0Q]

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.

An adult female Cottony cushion scale, Icerya purchasi (Hemiptera: Monophlebidae) with a small egg sac on a stem of North Island Broom, Carmichaelia australis (Leguminosae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2R0G]

An adult female Cottony cushion scale, Icerya purchasi (Hemiptera: Monophlebidae) and egg sac on a stem of Karo, Pittosporum crassifolium (Pittosporaceae): note the white wax on the body of the female. Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2R0F]

An immature adult female Cottony cushion scale, Icerya purchasi (Hemiptera: Monophlebidae) on a stem of Melicope simplex (Rutaceae). Creator: Darren Snaith. © Plant & Food Research. [Image: 2R07]

A large nymph or young adult female Cottony cushion scale, Icerya purchasi (Hemiptera: Monophlebidae) on a leaf. Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2R0I]

No pathogens of Cottony cushion scale are known in New Zealand.

Parasitoids

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.

Predators

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.

Two larvae of Cottony cushion scale parasitoid, Cryptochaetum iceryae (Diptera: Cryptochetidae) dissected from female Cottony cushion scale, Icerya purchasi (Hemiptera: Monophlebidae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2QZV]

Two empty pupae of Cottony cushion scale parasitoid, Cryptochaetum iceryae (Diptera: Cryptochetidae) in a dead female Cottony cushion scale, Icerya purchasi (Hemiptera: Monophlebidae): note the openings through which the adult flies emerged. Creator: Tim Holmes. © Plant & Food Research. [Image: 2QZU]

Pupae and an adult Cottony cushion scale parasitoid, Cryptochaetum iceryae (Diptera: Cryptochetidae) with the remains of a female Cottony cushion scale, Icerya purchasi (Hemiptera: Monophlebidae). Creator: Tim Holmes. © Plant & Food Research. [Image: 2QZS]

Adult Cottony cushion scale parasitoid, Cryptochaetum iceryae (Diptera: Cryptochetidae). Creator: Tim Holmes. © Plant & Food Research. [Image: 2QZP]

An immature adult female Cottony cushion scale, Icerya purchasi (Hemiptera: Monophlebidae) on a stem of Melicope simplex (Rutaceae): note the swollen body that indicates that it has been parasitised. Creator: Darren Snaith. © Plant & Food Research. [Image: 2R08]

A female Cottony cushion scale, Icerya purchasi (Hemiptera: Monophlebidae) with an exit hole of a wasp parasitoid (Hymenoptera). Creator: Nicholas A. Martin. © Nicholas A. Martin. [Image: 2R0N]

Adult eleven-spotted ladybird, Coccinella undecimpunctata (Coleoptera: Coccinellidae) on a lettuce leaf. Creator: Plant & Food Research Photographer. © Plant & Food Research. [Image: 159M]

A fully grown larva of eleven-spotted ladybird, Coccinella undecimpunctata (Coleoptera: Coccinellidae). Creator: Tim Holmes. © Plant & Food Research. [Image: 159Q]

Adult cardinal ladybird, Rodolia cardinalis (Coleoptera: Coccinellidae), pinned specimen. Creator: Birgit E Rhode. © Landcare Research. [Image: 2AW4]

Adult cardinal ladybird, Rodolia cardinalis (Coleoptera: Coccinellidae), pinned specimen. Creator: Birgit E Rhode. © Landcare Research. [Image: 2AW5]

Adult Koebele’s ladybird, Rodolia koebelei (Coleoptera: Coccinellidae). Creator: Minna Personen. © Plant & Food Research. [Image: 2AW2]

Larva of Koebele’s ladybird, Rodolia koebelei (Coleoptera: Coccinellidae). Creator: Tim Holmes. © Plant & Food Research. [Image: 2D66]

Young larva of Koebele's ladybird, Rodolia koebelei (Coleoptera: Coccinellidae) feeding on cottony cushion scale, Icerya purchasi (Hemiptera: Monophlebidae), the black arrow points to ladybird larva. Creator: Minna Personen. © Plant & Food Research. [Image: 2D6P]

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.

A female of Cottony cushion scale, Icerya purchasi (Hemiptera: Monophlebidae) on a leaf of Coprosma grandifolia (Rubiaceae): note the large distinctive white, fluted egg sac. Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2QZY]

Nymphs of Cottony cushion scale, Icerya purchasi (Hemiptera: Monophlebidae) on a leaf of Lemonwood, Pittosporum eugenioides (Pittosporaceae): note the white moulted skins. Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2QZZ]

Female Cottony cushion scale, Icerya purchasi (Hemiptera: Monophlebidae) on a stem of Lemonwood, Pittosporum eugenioides (Pittosporaceae): note the white, fluted egg sac. Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2R00]

A nymph of Cottony cushion scale, Icerya purchasi (Hemiptera: Monophlebidae) on a stem of Coastal tree daisy, Olearia solandri (Compositae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2R02]

Female Cottony cushion scale, Icerya purchasi (Hemiptera: Monophlebidae) on a stem of Coastal tree daisy, Olearia solandri (Compositae): note the white, fluted egg sac. Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2R03]

Nymphs of Cottony cushion scale, Icerya purchasi (Hemiptera: Monophlebidae) on a leaf of Tree nettle, Urtica ferox (Urticaceae): note the white moulted skins. Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2R04]

Female Cottony cushion scale, Icerya purchasi (Hemiptera: Monophlebidae) on a stem of Tree nettle, Urtica ferox (Urticaceae): note the white, fluted egg sac. Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2R06]

An adult female Cottony cushion scale, Icerya purchasi (Hemiptera: Monophlebidae) with a small egg sac on a stem of North Island Broom, Carmichaelia australis (Leguminosae). Creator: Nicholas A. Martin. © Plant & Food Research. [Image: 2R0G]

An adult female Cottony cushion scale, Icerya purchasi (Hemiptera: Monophlebidae) on a stem of Ngaio, Myoporum laetum (Scrophulariaceae): note the white, fluted egg sac. Creator: Nicholas A. Martin. © Nicholas A. Martin. [Image: 2R0M]

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.