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Species Page

Seychelles scale

Icerya seychellarum
This information is part of a full datasheet available in the Crop Protection Compendium (CPC). Find out more information on how to access the CPC.
©CAB International. Published under a CC-BY-NC-SA 4.0 licence.

Distribution

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Host plants / species affected

Main hosts

show all species affected
Acacia (wattles)
Albizia
Annona
Artocarpus (breadfruit trees)
Artocarpus integer (champedak)
Casuarina equisetifolia (casuarina)
Citrus
Cocos nucifera (coconut)
Ficus
Grevillea robusta (silky oak)
Magnolia
Persea americana (avocado)
Psidium (guava)
Psidium guajava (guava)
Pyrus (pears)
Rosa (roses)

List of symptoms / signs

Leaves - abnormal leaf fall
Leaves - honeydew or sooty mould
Leaves - honeydew or sooty mould
Stems - external feeding
Stems - honeydew or sooty mould
Whole plant - dwarfing

Symptoms

Sap depletion may lead to leaf drop and stunted growth. As with most sap-sucking insects, the production of honeydew leads to growth of sooty mould which in turn reduces plant respiration and photosynthesis.

Prevention and control

Introduction

As with most scale insects, chemical methods of control are largely ineffective due to the waxy covering of these insects. However natural enemies have proved effective in many instances.

Biological Control

Vedalia (Rodolia cardinalis), the ladybird predator, successfully regulated Icerya purchasi on citrus in California, USA, and has also proved to be of varying degrees of effectiveness against I. seychellarum. It has been reported as effective in Japan (Kuwana, 1922), the Seychelles (Versey-Fitzgerald, 1953), American Samoa (Dumbleton (1957), Cook Islands (Walker and Deitz, 1977), Fiji (Swaine, 1971), French Polynesia (Reboul, 1976) and Micronesia (Beardsley, 1966), but ineffective in Mauritius (Moutia and Mamet, 1946) and South Africa (Bedford, 1965). Interactions between I. seychellarum and ants may affect the efficiency of insect predators (Hill and Blackmore, 1980)Laboratory experiments have indicated that this predator can only live on I. seychellarum for three generations (Moutia and Mamet, 1946).

Other, more locally distributed ladybird predators have also been reported as control agents of limited effectiveness including Rodolia limbatus in Japan (Thorpe, 1934) and R. chermisina in Mauritius (Moutia and Mamet, 1946).

More effective control in Mauritius has been achieved by the introduction of the dipteran parasite Chryptochetum monophlebi from Madagascar in 1952 (Bedford, 1956).

Impact

I. seychellarum is a pest of guava, citrus, breadfruit, avocado, jackfruit, palms and roses in a number of Pacific Islands, where it has been recorded killing trees (Williams and Watson, 1990), and in the Seychelles, the Mascarene Islands and Japan. Heavy infestations have been recorded on Australian chestnut trees (Castanospermum australe) dropping copious amounts of honeydew onto cars parked beneath, but causing no apparent damage to the trees (Bedford, 1965).

Experimental removal of I. seychellarum with insecticides showed that 0.7 mg/cm² of scale insects reduced leaf growth by 52% (Newbery, 1980).