PEST

NAME
Cottonycushion Scale
Icerya purchasi

ORDER
Hemiptera

FAMILY
Margarodidae

Description of the Pest
This pest is also known as Ribbed Scaleor Bark-louse. The small soft bodied female is oval shaped, reddish-brown, and produces an extended fluted egg sack up to 10mm long that is covered with white, waxy threads. The crawlers are red with dark legs and the adult males are winged. The nymphs infest the ribs and veins of leaves, sucking the sap. Adults and nymphs suck sap with piercing and sucking mouth-parts and ants are attracted to the honeydew produced by feeding nymphs.

     
               Image by B. Sonsie

Appearance and Distribution of the Pest
This insect has a Hemimetabolouslife cycle, ie. When the immature nymphsresemble the adults.
Adults appear during the warmer months and infest twigs branches and are found on the trunks of some trees. Ants will usually be present as feeding nymphs produce honeydew, as will the Verdalia ladybeetle, (Rodolia cardinalis),which feeds on the nymphs.
This Australian native insect has been introduced to many countries such as the USA, India, Egypt and South Africa and was only brought under control by the introduction of the Verdalia ladybeetle.

Period of Activity
There are usually two hatches each year, in early spring and late summer.

Susceptible Plants
There are many plants that are attacked by this insect including Australian native species such as Acacia,Eucalyptus, Pittosporum, Hakeaand Grevilleas.
Ornamental trees and shrubs are also attacked including fruit trees and citrus,Liquidambar, Salix, Nerium, Magnolia, and Rosaspecies.
Palmsuch as Archontophoenixand Howeaspecies are also attacked particularly when grown as an indoor or glasshouse specimen.

Damage Caused
Heavy infestations may cause die-back, particularly where natural predators are absent (eg in glass-houses). The excretion of honeydew promotes sooty mold that restricts the leaves capability to photosynthesize.

Cultural Control
Dead or damaged parts of the plant should be removed and destroyed including fallen fruit. Small infestations may be removed by hand or squashed on the stems. Healthy plants are less susceptible to attack, so maintain vigour of the plant and avoid using high-nitrogen fertiliser that produces excessive soft young growth.
When pruning susceptible plants paint the cuts with antifungal sealant paint as scale insects are attracted to the sweet smell of the sap. This will reduce the infection rate of the plant.

BiologicalControl
Natural predators such as parasitic wasps may reduce numbers of active nymphs; parasitic wasps are bred commercially in some areas for this purpose and the main natural predator is the Verdalialadybeetle, (Rodolia cardinalis).It should be noted, however, that wasps would avoid dusty conditions.
Other predators that assist in control are assassin bugs, lacewings, hover flies and scale eating caterpillars. A variety of birds also attack scales.

Chemical Control
Normally not necessary.