Preferred Scientific Name
- Icerya samaraia (Morrison, 1927)
Preferred Common Name
- steatococcus scale
Other Scientific Names
- Steatococcus samaraius Morrison, 1927
International Common Names
- English: fluted scale; giant scale
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The scale insect Icerya samaraia (formerly Steatococcus samaraius) occurs in the Australasian, Oriental and Oceanic zoogeographic regions. It has a wide host range which includes mostly woody plant species in 40 genera belonging to 25 families. It is a minor pest of citrus, banana, coconut, guava, papaya, cocoa, pigeon pea and other plants, including forest and ornamental trees. Populations of I. samaraia are apparently being kept under control on the Palau Islands in the western Pacific Ocean by natural enemies, particularly by the introduced coccinellid Rodolia pumila. I. samaraia can be transported on infested plant materials because of its small size and habit of feeding in concealed areas, making it a potential threat as an invasive species.
The species was originally described as S. samaraius in the family Margarodidae from an unstated host in Papua New Guinea (Morrison, 1927). The taxonomy of the scale insect tribe Iceryini was recently revised by Unruh and Gullan (2008a) based on a molecular phylogenetic hypothesis and supporting morphological evidence. This revision led to a significant reorganization of species in three of the five iceryine genera: Crypticerya Cockerell, Gigantococcus Pesson & Bielenin and Icerya Signoret. During this reorganization, Steatococcus samaraius was transferred to Icerya, as Icerya samaraia (Morrison, 1927) comb. nov., in the family Monophlebidae (Unruh and Gullan, 2008a,b; Ben-Dov et al., 2014). At the time of writing, the species is still listed as Steatococcus samaraius Morrison, 1927 in a number of websites (GBIF, 2014; Roskov et al., 2014).
The live adult female is 2.9-5.0 mm long and 2.4-4.0 mm wide, with a pale yellow oval body covered in white wax or sulfur-yellow flocculent wax tinged with white. In the slide-mounted adult female, the antennae each have 9-11 segments and there are three pairs of abdominal spiracles towards the apex of the abdomen. The center of the abdominal venter becomes invaginated to form a marsupium into which the vulva opens, and there is a marsupial band of simple multilocular pores along the lip of the marsupium, which becomes sclerotized with age.
A full description of the adult female of I. samaraia (as Steatococcus samaraius) is provided in Williams and Watson (1990) and Unruh and Gullan (2008a). Identification keys are given in Morrison (1928) (for species of Steatococcus) and Unruh and Gullan (2008a) (for species of Icerya). Authoritative identification requires study of slide-mounted adult females under a compound light microscope. The body surface is covered with hair-like setae, the longest of which form clusters around the margin. Open-centre pores form clusters of 2-6 around the body margin. Simple multilocular pores, each with an elongate or bilocular (rarely trilocular) centre, are scattered across the dorsal surface. Simple multilocular pores, each 7-9 μm in diameter, are also scattered in the marsupial cavity and around the edges of the marsupial band, also sparsely on the ventral surface (Williams and Watson, 1990; Unruh and Gullan, 2008a). There are three oval-to-round cicatrices (papillose structures) that form a transverse row or semi-circle on the ventromedial abdomen posterior to the vulvar opening.
I. samaraia was described as a new species from specimens collected in Papua New Guinea in 1927. The species was subsequently reported from Yap in the Federated States of Micronesia, New Caledonia and parts of Indonesia. I. samaraia was first recorded from the Solomon Islands (host not stated) in 1954 (Beardsley, 1966) and from Guam on monkeypod (species not given but presumably Albizia saman (Jacq.) Merr., Leguminosae) in March 1985 (Beardsley, 1986; Schreiner and Nafus, 1986). In 1992 I. samaraia was recorded in Guam and Rota, Northern Mariana Islands on Serianthes nelsonii, a rare leguminous tree endemic to these islands (Wiles et al., 1996). I. samaraia was reported as a new record from Sulawesi, Indonesia in November 2011 (Gavrilov-Zimin, 2013) although Reyne (1965) had recorded the species from North Celebes (Sulawesi) consdierably earlier (Williams and Watson, 1990).
Serious infestations of I. samaraia on an unspecified species of Phyllanthus were reported in Singapore in a newsletter published in 2013 (Agri-Food & Veterinary Authority of Singapore, 2013). I. samaraia has been intercepted at US ports-of-entry on plant materials from Guam (Areca), Indonesia (Areca), Malaysia (Cordyline and Nomaphila), Papua New Guinea (Begonia), Palau (Areca) and Taiwan (palm) (Miller et al., 2014a).
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.Last updated: 10 Jan 2020
|Continent/Country/Region||Distribution||Last Reported||Origin||First Reported||Invasive||Reference||Notes|
|Indonesia||Present||Present based on regional distribution.|
|Federated States of Micronesia||Present||Native||Yap; Original citation: Beardsely (1966)|
|Northern Mariana Islands||Present||Rota|
|Papua New Guinea||Present||Native|
In common with other scale insects, I. samaraia may be transported on plant materials because of its relatively small size and habit of feeding in concealed areas, making it a potential threat to areas where it is not yet present (Miller et al., 2014b). I. samaraia has been intercepted at US ports-of-entry on plant materials from Guam (Areca), Indonesia (Areca), Malaysia (Cordyline and Nomaphila), Papua New Guinea (Begonia), Palau (Areca) and Taiwan (palm) (Miller et al., 2014a).
|Terrestrial||Managed||Cultivated / agricultural land||Present, no further details||Harmful (pest or invasive)|
|Terrestrial||Managed||Protected agriculture (e.g. glasshouse production)||Present, no further details||Harmful (pest or invasive)|
|Terrestrial||Managed||Managed forests, plantations and orchards||Present, no further details||Harmful (pest or invasive)|
|Terrestrial||Natural / Semi-natural||Natural forests||Present, no further details||Harmful (pest or invasive)|
|Terrestrial||Natural / Semi-natural||Scrub / shrublands||Present, no further details||Harmful (pest or invasive)|
I. samaraia has been reported on mostly woody plant species in 40 genera belonging to 25 families from the Australasian and Oriental zoogeographic regions (Miller et al., 2014a).
|Annona muricata (soursop)||Annonaceae||Other|
|Cajanus cajan (pigeon pea)||Fabaceae||Main|
|Carica papaya (pawpaw)||Caricaceae||Main|
|Casuarina equisetifolia (casuarina)||Casuarinaceae||Other|
|Cocos nucifera (coconut)||Arecaceae||Main|
|Colocasia esculenta (taro)||Araceae||Other|
|Epipremnum pinnatum (centipede tongavine)||Araceae||Other|
|Eucalyptus deglupta (kamarere)||Myrtaceae||Other|
|Hibiscus rosa-sinensis (China-rose)||Malvaceae||Other|
|Hibiscus tiliaceus (coast cottonwood)||Malvaceae||Other|
|Mangifera indica (mango)||Anacardiaceae||Other|
|Mimosa pigra (giant sensitive plant)||Fabaceae||Other|
|Pinus caribaea (Caribbean pine)||Pinaceae||Other|
|Pinus merkusii (Tenasserim pine)||Pinaceae||Other|
|Psidium guajava (guava)||Myrtaceae||Main|
|Schinus terebinthifolius (Brazilian pepper tree)||Anacardiaceae||Other|
|Tephrosia candida (white tephrosia)||Fabaceae||Other|
|Theobroma cacao (cocoa)||Malvaceae||Main|
Most damage to plants is caused by the early immature stages of I. samarai, which feed on the leaf undersides, settling in rows along the midrib and veins, and on smaller twigs. The older nymphs feed on larger twigs, and as adults they settle on larger branches and the trunk. Damage to plants results from phloem sap depletion during feeding, leading to shoots drying up and dying. Trees that are badly attacked suffer partial defoliation and a general loss of vigour. The insects dischargesugary honeydew, which can be copious in large colonies and may foul plant surfaces. Besides direct damage by feeding, indirect damage can result from the development of black sooty mould on the honeydew on leaf surfaces, blocking light and air from the plant, leading to a reduction in photosynthesis (Beardsley, 1955).
|Growing point / dieback|
|Growing point / external feeding|
|Growing point / honeydew or sooty mould|
|Growing point / wilt|
|Leaves / abnormal leaf fall|
|Leaves / external feeding|
|Leaves / honeydew or sooty mould|
|Leaves / wilting|
|Stems / external feeding|
|Stems / honeydew or sooty mould|
|Stems / wilt|
|Whole plant / external feeding|
Not much has been published on the reproductive biology of I. samaraia and it is difficult to generalize from other members of the family or genus because the mode of reproduction varies between species. A number of species of scale insect reproduce parthenogenetically, and functional hermaphroditism has been reported in some species of Icerya (Hughes-Schrader, 1930; Gullan and Kosztarab, 1997). Adult males are short-lived and weak fliers, so they usually mate only with local females (Gullan and Kosztarab, 1997).
Adult females of I. samaraia have a marsupium, an internal brood chamber within which eggs are laid and first-instar nymphs (crawlers) hatch and emerge (Unruh and Gullan, 2008a,b). The first-instar nymphs, or crawlers, are the main agents of dispersal in scale insects and have relatively well-developed antennae and legs. They disperse by walking and may also be carried to new feeding sites by the wind (Hill, 1980; Gullan and Kosztarab, 1997) or by ants (Wiles et al., 1996; Gullan and Kosztarab, 1997). If conditions are favourable they settle on the natal host plant, often close to their mother (Gullan and Kosztarab, 1997).
Physiology and Phenology
Scale insects have neotenous adult females (that is, they retain the immature external morphology even when sexually mature) and winged but non-feeding adult males. Species of Monophlebidae generally have four developmental stages in the female and five in the male. Nymphs of all stages feed actively, sucking plant juices through a set of stylets, except for the non-feeding third and fourth instars of males which are termed the ‘prepupal’ and ‘pupal’ instars. Adult females are usually stationary or completely immobile on the host plant. They produce a waxy secretion, which may provide a protective covering against water loss, wet conditions, attack by natural enemies and contamination by their own honeydew (Gullan and Kosztarab, 1997).
The honeydew produced by I. samaraia attracts ants, which live in close association with the scale insects and protect them from predators and parasitoids. In the Solomon Islands, I. samaraia has been reported being tended by the ant Oecophyllasmaragdina on the aroid Epipremnum pinnatum (Brown, 1959) and by the ants O. smaragdina and Anoplolepis longipes on cocoa (Theobroma cacao), Macaranga aleuritoides and Macaranga tanarius (Bigger, 1988).
|Af - Tropical rainforest climate||Preferred||> 60mm precipitation per month|
The coccinellids Rodolia pumila and Cryptolaemus montrouzieri and an undetermined entomophagous fungus were reported as natural enemies of I. samaraia on the Palau Islands (Beardsley, 1955). These coccinellids were introduced to Palau to control Icerya species and became established around the mid-20th century (Beardsley, 1955, 1966; Schreiner, 1989; Waterhouse, 1993).
Besides the introduced coccinellids, several other natural enemies have been found attacking the related species Icerya aegyptiaca in Micronesia, including adults and larvae of green lacewings (Chrysopa spp.) and the coccinellids Harmonia arcuata and Coelophora inaequalis. A species of the coccinellid genus Scymnus has been reported as a fairly effective natural enemy of I. purchasi (cottony cushion scale) on Guam.
|Plant parts liable to carry the pest in trade/transport||Pest stages||Borne internally||Borne externally||Visibility of pest or symptoms|
|Leaves||adults; nymphs; pupae||Yes||Pest or symptoms usually visible to the naked eye|
|Seedlings/Micropropagated plants||adults; nymphs; pupae||Yes||Pest or symptoms usually visible to the naked eye|
|Stems (above ground)/Shoots/Trunks/Branches||adults; nymphs; pupae||Yes||Pest or symptoms usually visible to the naked eye|
I. samaraia is considered to be a minor pest of citrus, banana, coffee, coconut, guava, papaya, cocoa, pigeon pea and other woody plants, including forest and ornamental trees. In Palau I. samaraia was reported to be kept under control on banana, coconut and other plants by natural enemies and was not regarded as a major pest (Beardsley, 1955, 1966; Nafus, 1997, cited in Williams et al., 2006). Serious infestations of I. samaraia on an unspecified species of Phyllanthus were reported in Singapore in a newsletter published in 2013 (Agri-Food & Veterinary Authority of Singapore, 2013).
Foliage and stems should be inspected for lumps of white or yellow wax secreted by scale insects, symptoms of pest attack, attendent ants, sticky honeydew and sooty mould growth on leaves. A user-friendly, online tool has been produced for use at US ports-of-entry to help with the identification of potentially invasive scale insect species (Miller et al., 2014a,b).
Only three described Icerya species form a marsupium (an internal brood chamber): I. assamensis, I. nudata and I. samaraia. I. assamensis differs from I. nudata and I. samaraia by the absence of open-centre pores in the adult female (Unruh and Gullan, 2008a). I. samaraia and I. nudata, the only two species in the I. nudata group, are the only marsupium-forming species that have open-centre pores present on the derm. They differ from each other by the shape and size of the open-centre pores. I. samaraia has large pores (20-24 μm in diameter), each with an elongate or bilocular centre (very rarely a triangular cleft) and with 14-16 tightly spaced outer loculi, whereas the open-centre pores of I. nudata are smaller (12-15 μm in diameter), each with a faint triangular cleft and there are fewer (5-7) widely spaced outer loculi (Unruh and Gullan, 2008a).
Due to the variable regulations around (de)registration of pesticides, your national list of registered pesticides or relevant authority should be consulted to determine which products are legally allowed for use in your country when considering chemical control. Pesticides should always be used in a lawful manner, consistent with the product's label.
The coccinellid predator Rodolia pumila is believed to be specific to Icerya species and closely related scale insects, and has been used successfully for the biological control of the related species Icerya aegyptiaca on some islands of Micronesia (Schreiner, 1989; Waterhouse, 1993).
Of three species of Rodolia (R. pumila, R. cardinalis and R. breviuscula) introduced to the oceanic Pacific for the control of I. aegyptiaca, I. purchasi and I. seychellarum, only R. pumila became widely established on the high islands of Micronesia by the 1950s. R. pumila appears to have been less successful on low coral atolls, possibly after reducing the abundance of its hosts to such low levels that the coccinellid was unsustainable (Beardsley, 1955; Schreiner, 1989; Waterhouse, 1993). This leads to a boom and bust cycle, with predatory beetles disappearing for long enough in some locations for damaging populations of I. aegyptiaca to develop for several years at a time (Waterhouse, 1993). R. pumila is also reported to keep populations of I. samaraia under control in Palau (Beardsley, 1966).
Another coccinellid, Cryptolaemus montrouzieri, was introduced for the control of Icerya spp. in Palau and Saipan (Northern Mariana Islands) and became established by 1940 (Schreiner, 1989; Waterhouse, 1993). It has been recorded attacking I. samaraia in Palau (Beardsley, 1955).
Chemical control of I. samaraia is difficult because the waxy layer the insects produce protects the insects from pesticide sprays. The crawlers are least well protected, and may be treated with organophosphates such as acephate, but as these chemicals can be toxic to natural enemies they are best avoided (Agri-Food & Veterinary Authority of Singapore, 2013). Natural enemies provide the most effective method of control.
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13/03/15 Original text by:
Angela Whittaker, Consultant, UK
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