Since Clare Morales revision of New Zealand Margarodidae in , 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 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.

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Cottony cushion scale, Icerya purchasi , can infest a number of woody ornamentals and certain crops Figure 1. Common hosts in California are citrus, cocculus, nandina, and pittosporum. Its cottony egg sac and profuse honeydew production make cottony cushion scale easy to spot in the landscape. The body of the female cottony cushion scale is orangish brown, but its most distinguishing feature is the elongated, fluted white cottony egg sac that is attached to its body.

Eggs hatch into crawlers Figure 3 in a few days during warm weather but take up to two months to hatch in winter. The crawlers are red with black legs and antennae. They settle along leaf veins and begin to produce the white cottony secretion they are known for.

In order to increase in size, scales shed their outer skin molt and grow a new, larger covering. Each time the scale molts, it leaves behind its white, cottony molting skin Figure 4. Immature scales look reddish for a short period of time before they begin producing more cottony secretions. Second-instar nymphs settle on twigs and leaves, usually along leaf veins Figure 5. Third-instar nymphs move to branches Figure 6. Adults may be found on branches or on the trunk of trees.

Cottony cushion scale has two to three generations a year. Unlike most other scales, it retains its legs and its mobility throughout its life. Cottony cushion scale completes its life cycle in three months during warm weather conditions. For additional photographs of each life stage of cottony cushion scale, consult Stages of the Cottony Cushion Scale Icerya purchasi and its Natural Enemy, the Vedalia Beetle Rodolia cardinalis.

Like other scales, cottony cushion scale decreases the vitality of its host by sucking phloem sap from the leaves, twigs, branches, and trunk. Feeding can result in defoliation and dieback of twigs and small branches when infestations are extremely heavy Figure 7.

Heavy populations can severely reduce the yield of citrus trees. Like soft scales, cottony cushion scale excretes honeydew, which is usually accompanied by blackish sooty mold growth and ants Figure 8. Unless disrupted by insecticides, dust, or ants, natural enemies provide excellent control of cottony cushion scale.

An exception is on Cocculus laurifolius laurel-leaf snailseed or laurel leaf cocculus ; it is often highly infested with cottony cushion scale, especially when grown away from the coast, because scale-feeding vedalia beetles avoid this plant.

Cottony cushion scale is usually well controlled by two introduced natural enemies. The most famous one is the vedalia beetle , Rodolia cardinalis , Figure 9. Adult female beetles lay their oblong red eggs underneath the female scale or attached to her egg sac. The newly hatched reddish beetle larvae chew their way into the egg sac and feed on scale eggs and crawlers.

Larvae molt two times and gradually increase in size. Mature larvae Figure 10 and adult beetles feed on all scale stages. The fourth, and last, larval instar stops feeding, crawls toward the outside of the tree, and attaches its posterior end to a leaf in preparation for pupation. Reddish beetle pupae develop within the grayish skin of the last larval instar Figure The entire life cycle of the vedalia beetle is five to six weeks in warm weather.

The other important natural enemy, the parasitic fly Cryptochaetum iceryae Figure 12 , deposits one to four eggs inside each second-instar, third-instar, or adult female scale body. The eggs hatch into larvae that feed within the scale.

After four molts, the larvae pupate inside the scale. When the adult fly emerges, it creates a round emergence hole, easily seen in the scale. The life cycle of the Cryptochaetum fly is about four weeks in warm weather.

Both the vedalia beetle and Cryptochaetum are active in coastal areas; the vedalia beetle is also abundant in Southern California desert regions and is the predominant species in interior areas of California. Both of these natural enemies can be extremely effective in controlling cottony cushion scale because of their short generation time four to six weeks and host specificity, attacking only cottony cushion scale.

Conserve natural enemies of cottony cushion scale by controlling ants and dust and by avoiding the use of persistent insecticides.

Inspect female scales for Cryptochaetum emergence holes. Ants protect scale insects from predators and parasites in order to farm the honeydew the scales produce. To improve biological control, keep ants out of trees and shrubs by banding the trunks with sticky substances such as Tanglefoot or by using ant baits. Protect young or sensitive trunks, especially citrus, from possible injury by wrapping the trunk with a collar of duct tape or fabric tree wrap and coating this with the sticky material.

Check the sticky material every week or two and stir it with a stick to prevent the material from becoming covered with debris that ants can cross. Alternatively, pesticide baits such as ant stakes may be placed near nests or on ant trails beneath plants.

For the most effective and economical control, treat in early spring when ant populations are active but before they become heavy. For more information, see Pest Notes: Ants. The females and their eggs are protected by both the cottony egg sac and their position inside the canopy of the tree, making this pest difficult to treat. You can use traps made of double-sided sticky tape to determine when crawlers are hatching.

Before crawlers begin to emerge in spring, tightly encircle several twigs or branches near adult female scale with transparent tape that is sticky on both sides, such as Scotch double-sided tape.

Change the tape at regular intervals, about once a week, and examine it with a hand lens to identify the crawlers. Once eggs begin hatching, scale crawlers get stuck on the tape and appear as red or orange specks. Spray after you observe a sharp increase in crawler production. Natural enemies are the best method for controlling cottony cushion scale, so look carefully for their presence and avoid insecticides if you find evidence of natural enemies attacking cottony cushion scale.

If natural enemies are absent, the infestation is intolerable, and the population is in the treatable crawler stage, the organophosphates malathion or acephate can be effective. Both of these materials can be quite toxic to natural enemies, honey bees, and nontarget organisms; acephate is allowed only for use on ornamentals. Horticultural oil can also be applied to manage the crawler stage and is least disruptive of natural enemies or bees.

To make matters worse, imidacloprid is very toxic to vedalia beetles. The beetles are poisoned when they feed on cottony cushion scale that have ingested imidacloprid. Dreistadt, S. Clark, and M. Oakland: Univ. Grafton-Cardwell, E. Pest Notes: Ants. All rights reserved. For noncommercial purposes only, any Web site may link directly to this page. Unfortunately, we cannot provide individual solutions to specific pest problems.

See our Home page , or in the U. Agriculture and Natural Resources, University of California. Figure 1. Colony of cottony cushion scale. Figure 2. Figure 3. Cottony cushion scale crawlers. Figure 4. Each time a scale molts, it leaves behind its white, cottony molting skin. Figure 5. Cottony cushion scale second-instar nymphs. Figure 6. A third-instar nymph. About Pest Notes Publication Glossary. Figure 7. Mature cottony cushion scale females on bark. Figure 8. Cottony cushion scale is usually accompanied by blackish sooty mold growth as show on these citrus leaves.

Figure 9. Adult cottony cushion scale female with an adult vedalia beetle in the foreground and vedalia beetle nymphs and eggs on its back. The adult female beetle lays eggs underneath the scale or attached to scale egg sacs.

The larval and adult stages of the beetle feed on scale eggs and the adult scale. Mature vedalia beetle larva feeding on cottony cushion scale. Figure Vedalia pupa. Adult parasitic fly Cryptochaetum iceryae left and female cottony cushion scales with parasite emergence holes right.


Citrus Pests

The genus Icerya has been poorly studied and it is possible that there are other species similar to I. Rao reviewed the known species of Icerya living in the Oriental Region, and a revision of the known species in Australia is currently in progress. 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.


Common Name

The cottony cushion scale was described by Maskell from specimens sent to him by Dr. Purchas from Auckland, New Zealand. The host was kangaroo acacia and the insect was named for Dr. This scale is apparently native to Australia and made its way to California on acacia plants around or and in about ten years was causing damage to citrus groves in southern California Ebeling New control methods used first in California and later the rest of United States led to the implementation of biological control and legislative quarantine Ebeling Figure 1.


How to Manage Pests

The cottony cushion scale, Icerya purchasi , is considered to have originated in Australia. It was accidentally introduced to California in about and devastated the citrus industry there until a natural enemy from Australia was introduced in This was the first ever example of successful classical biological control. The cottony cushion scale has subsequently spread widely through most of the tropical and subtropical countries of the world. It is also periodically discovered in greenhouses in temperate regions, but is not generally a pest in these situations. As with all scale insects, the females do not have wings and look similar to the immature stages.


Cottony cushion scale

Cottony cushion scale, Icerya purchasi , can infest a number of woody ornamentals and certain crops Figure 1. Common hosts in California are citrus, cocculus, nandina, and pittosporum. Its cottony egg sac and profuse honeydew production make cottony cushion scale easy to spot in the landscape. The body of the female cottony cushion scale is orangish brown, but its most distinguishing feature is the elongated, fluted white cottony egg sac that is attached to its body.

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