Cottony cushion scale—Icerya purchasi
This sucking insect (Monophlebidae, formerly Margarodidae) can occur on many woody species. Its common hosts include citrus, cocculus, nandina, and pittosporum.
Identification
The female body is orangish brown, and at maturity it is distinguished by its elongated, fluted, white cottony egg sac, up to 1/2 inch long. Eggs are oblong and red. The crawlers (mobile, first-instar nymphs) are red with dark legs and antennae. Once crawlers settle and begin feeding, they excrete a covering of yellowish to white wax. All nymphal instars are reddish shortly after molting, before they produce cottony secretions.
Life cycle
First- and second-instar nymphs settle on twigs and leaves, usually along leaf veins. Third instars occur on branches. Mature female scales occur mostly on large branches or the trunk. The loose, white cocoon of immature males and the minute, red, winged adult male are rarely seen. Cottony cushion scales retain legs and can move throughout their life. The scale has two to three generations per year.
Damage
Cottony cushion scale sucks phloem sap from the leaves, twigs, branches, and trunk. The scale usually occurs at very low densities unless its natural enemies are disrupted, for example, by application of certain insecticides. An exception is on laurel-leaf snailseed, Cocculus laurifolius, which often is highly infested with cottony cushion scale; the scale-eating vedalia lady beetle avoids this plant.
When infestations are extremely heavy, feeding by the scales can result in defoliation and dieback of twigs and small branches and severely reduce the yield of citrus trees. Cottony cushion scales excrete honeydew, which causes blackish sooty mold growth and attracts ants.
Solutions
A parasitic fly, Cryptochaetum iceryae (Cryptochaetidae), and a lady beetle, the vedalia, Rodolia cardinalis, are the most important natural enemies of cottony cushion scale. Both Cryptochaetum and vedalia are common where the scale occurs in coastal California. Vedalia predominates in inland areas.
The red and black adults of vedalia feed voraciously on cottony cushion scales. The young, reddish vedalia larvae feed on scale eggs; more mature larvae feed on all scale stages.
The orangish larvae of the parasitic Cryptochaetum feed within the scale; later their dark, oblong pupal cases may be seen there. This fly produces up to eight generations per year.
Conserve natural enemies by controlling ants and dust and by avoiding use of broad-spectrum, residual insecticides, which can have a severe adverse effect on vedalia. If scales cannot be tolerated until natural enemies become abundant, apply horticultural oil to deciduous hosts during the dormant season or spray foliage when the tiny, reddish scale crawlers and young nymphs are the predominate stages.
See Pest Notes: Cottony Cushion Scale for more information. For photographs of each life stage, consult Stages of the Cottony Cushion Scale (Icerya purchasi) and its Natural Enemy, the Vedalia Beetle (Rodolia cardinalis) .
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Females with white egg sacs
Red crawlers with black legs
Second-instar nymphs
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