Scale insects
 
 
Scale insects are in the superfamily Coccoidea of the Hemiptera, suborder Sternorrhyncha.  They live under a tough waxy secretion often referred to as a shell or scale. Legs, antennae or wings are often not visible, and some species resemble limpets!  They suck sap from a wide range of plants.
 
Species in Britain and Ireland
More than 60 species have been identified in Britain and Ireland.  Many are introduced species that were originally brought in on garden plants.  Some are only found in glasshouses. Common species include the soft scale group, Coccus hesperidum agg. on many woody plants, especially Citrus, Ficus and bay tree; brown scale group, Parthenolecanium corni agg. on many shrubs, grape vine, plum and bush fruits; horse chestnut scale, Pulvinaria regalis, on maple species, lime trees, bay tree, horse chestnut and magnolia; cushion scale, Pulvinaria floccifera, on Camellia, Rhododendron, holly and Trachelospermum; hydrangea scale, Pulvinaria hydrangeae, on hydrangea, lime, maples, Prunus species and Viburnum; euonymus scale, Unaspis euonymi, on Euonymus japonicus; mussel scale, Lepidosaphes ulmi, on apple, box, Ceanothus and Cotoneaster.
 
 
Juniper scale insect Carulaspis juniperi                       Hydrangea scale Pulvinaria hydrangae on lime (Tilia sp)
 
Biology
Scale insects suck sap from foliage, usually on the underside, and from plant stems.  Some species, such as cushion scale and soft scale, excrete large quantities of a sugary excrement called honeydew.  This makes the upper surface of leaves sticky and allows the growth of sooty mould. Newly hatched scales will crawl around to find suitable feeding places but then remain stationary for most of the rest of their lives. 
 
 
Reproduction and life cycle
In many species of scale insects, males are rare or non-existent, with the females reproducing asexually.  Where both males and females occur, as in euonymus scale, the two sexes often differ in size, shape and colour.  When mature, adult males are small winged insects that emerge from under their scales to mate with the wingless females. The males often only live for a few days as adults.
 
Most scale insects deposit their eggs underneath their bodies and the covering scale.  Pulvinaria species, however, place their eggs in a white waxy secretion that can form a distinctive mound or band behind the scale.  Some species have several generations a year but most scales on outdoor plants have a single generation, with eggs laid in late spring and hatching in early summer.  The newly hatched nymphs crawl around for a while before settling down to feed. Most scale insects overwinter as young nymphs but some overwinter as adults.
 
Role of scale insects in gardens
Plants can generally cope with light scale insect loads however heavy infestations of scale insects can weaken plants to the extent of causing dieback.  Those species that produce honeydew spoil the appearance of plants, especially if sooty mould develops on the foliage.  Fortunately, in most years infestations are at a relatively low level and do not have a damaging impact.  Some ladybirds specialise in feeding on scale insects and their numbers are also reduced by various parasitic wasps.
 
Other sources of information
 
RHS web page on scale insects
 
Scientific paper
Malumphy, Chris & Badmin, John. (2012). Scale insects and whiteflies (Hemiptera: Coccoidea and Aleyrodoidea) of Watsonian Kent; with a discussion on the impact of naturalised non-native species. British Journal of Entomology and Natural History. 25. 15-49.
 
 
Page drafted by Andrew Halstead, reviewed by Andrew Salisbury, edited by Steve Head
 
 
Left: Horse chestnut scales and egg sacs on Acer trunk Centre:  Kidney spot ladybird adults with Euonymus scale insects  Right:  Rose scurfy scale insect  Aulacaspis rosae 
Left: Horse chestnut scales and egg sacs on Acer trunk   Centre:  Kidney spot ladybird adults with Euonymus scale insects  Right:  Rose scurfy scale insect  Aulacaspis rosae 
Juniper scale insect Carulaspis juniperi      Hydrangea scale Pulvinaria hydrangae                                                                              on lime (Tilia sp)
 
Biology
Scale insects suck sap from foliage, usually on the underside, and from plant stems.  Some species, such as cushion scale and soft scale, excrete large quantities of a sugary excrement called honeydew.  This makes the upper surface of leaves sticky and allows the growth of sooty mould. Newly hatched scales will crawl around to find suitable feeding places but then remain stationary for most of the rest of their lives. 
 
 
Reproduction and life cycle
In many species of scale insects, males are rare or non-existent, with the females reproducing asexually.  Where both males and females occur, as in euonymus scale, the two sexes often differ in size, shape and colour.  When mature, adult males are small winged insects that emerge from under their scales to mate with the wingless females. The males often only live for a few days as adults.
 
Most scale insects deposit their eggs underneath their bodies and the covering scale.  Pulvinaria species, however, place their eggs in a white waxy secretion that can form a distinctive mound or band behind the scale.  Some species have several generations a year but most scales on outdoor plants have a single generation, with eggs laid in late spring and hatching in early summer.  The newly hatched nymphs crawl around for a while before settling down to feed. Most scale insects overwinter as young nymphs but some overwinter as adults.
 
Role of scale insects in gardens
Plants can generally cope with light scale insect loads however heavy infestations of scale insects can weaken plants to the extent of causing dieback.  Those species that produce honeydew spoil the appearance of plants, especially if sooty mould develops on the foliage.  Fortunately, in most years infestations are at a relatively low level and do not have a damaging impact.  Some ladybirds specialise in feeding on scale insects and their numbers are also reduced by various parasitic wasps.
 
Other sources of information
 
RHS web page on scale insects
 
Scientific paper
Malumphy, Chris & Badmin, John. (2012). Scale insects and whiteflies (Hemiptera: Coccoidea and Aleyrodoidea) of Watsonian Kent; with a discussion on the impact of naturalised non-native species. British Journal of Entomology and Natural History. 25. 15-49.
 
 
Page drafted by Andrew Halstead, reviewed by Andrew Salisbury, edited by Steve Head
 
 
Scale insects
 
Scale insects are in the superfamily Coccoidea of the Hemiptera, suborder Sternorrhyncha.  They live under a tough waxy secretion often referred to as a shell or scale. Legs, antennae or wings are often not visible, and some species resemble limpets!  They suck sap from a wide range of plants.
 
Species in Britain and Ireland
More than 60 species have been identified in Britain and Ireland.  Many are introduced species that were originally brought in on garden plants.  Some are only found in glasshouses. Common species include the soft scale group, Coccus hesperidum agg. on many woody plants, especially Citrus, Ficus and bay tree; brown scale group, Parthenolecanium corni agg. on many shrubs, grape vine, plum and bush fruits; horse chestnut scale, Pulvinaria regalis, on maple species, lime trees, bay tree, horse chestnut and magnolia; cushion scale, Pulvinaria floccifera, on Camellia, Rhododendron, holly and Trachelospermum; hydrangea scale, Pulvinaria hydrangeae, on hydrangea, lime, maples, Prunus species and Viburnum; euonymus scale, Unaspis euonymi, on Euonymus japonicus; mussel scale, Lepidosaphes ulmi, on apple, box, Ceanothus and Cotoneaster.
 
 
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