''Pulvinaria regalis'' is a

species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...

scale insect Scale insects are small insects of the order Hemiptera, suborder Sternorrhyncha. Of dramatically variable appearance and extreme sexual dimorphism, they comprise the infraorder Coccomorpha which is considered a more convenient grouping than the ...

in the family

Coccidae The Coccidae are a family of scale insects belonging to the superfamily Coccoidea. They are commonly known as soft scales, wax scales or tortoise scales. The females are flat with elongated oval bodies and a smooth integument which may be cover ...

. Although it is commonly known as the horse chestnut scale, it affects other trees besides

horse chestnuts The genus ''Aesculus'' ( or ), with species called buckeye and horse chestnut, comprises 13–19 species of flowering plants in the family Sapindaceae. They are trees and shrubs native to the temperate Northern Hemisphere, with six species n ...

as well as many species of woody shrubs. Adults are normally all female and produce eggs by

parthenogenesis Parthenogenesis (; from the Greek grc, παρθένος, translit=parthénos, lit=virgin, label=none + grc, γένεσις, translit=génesis, lit=creation, label=none) is a natural form of asexual reproduction in which growth and development ...

. The insects are thought to have originated in Asia but arrived in Europe in the second half of the twentieth century.

Host species

''Pulvinaria regalis'' is known to be hosted by 65 species of plant from 25 families. The main species of tree which act as hosts for this scale insect are

horse chestnut The genus ''Aesculus'' ( or ), with species called buckeye and horse chestnut, comprises 13–19 species of flowering plants in the family Sapindaceae. They are trees and shrubs native to the temperate Northern Hemisphere, with six species n ...

sycamore Sycamore is a name which has been applied to several types of trees, but with somewhat similar leaf forms. The name derives from the ancient Greek ' (''sūkomoros'') meaning "fig-mulberry". Species of trees known as sycamore: * ''Acer pseudoplata ...

maple ''Acer'' () is a genus of trees and shrubs commonly known as maples. The genus is placed in the family Sapindaceae.Stevens, P. F. (2001 onwards). Angiosperm Phylogeny Website. Version 9, June 2008 nd more or less continuously updated since http ...

lime Lime commonly refers to: * Lime (fruit), a green citrus fruit * Lime (material), inorganic materials containing calcium, usually calcium oxide or calcium hydroxide * Lime (color), a color between yellow and green Lime may also refer to: Botany ...

elm Elms are deciduous and semi-deciduous trees comprising the flowering plant genus ''Ulmus'' in the plant family Ulmaceae. They are distributed over most of the Northern Hemisphere, inhabiting the temperate and tropical-montane regions of North ...

magnolia ''Magnolia'' is a large genus of about 210 to 340The number of species in the genus ''Magnolia'' depends on the taxonomic view that one takes up. Recent molecular and morphological research shows that former genera ''Talauma'', ''Dugandiodendro ...

bay A bay is a recessed, coastal body of water that directly connects to a larger main body of water, such as an ocean, a lake, or another bay. A large bay is usually called a Gulf (geography), gulf, sea, sound (geography), sound, or bight (geogra ...

and

dogwood ''Cornus'' is a genus of about 30–60 species of woody plants in the family Cornaceae, commonly known as dogwoods, which can generally be distinguished by their blossoms, berries, and distinctive bark. Most are deciduous trees or shrub ...

Distribution and habitat

''Pulvinaria regalis'' is thought to be native to Asia. It was first detected in Europe in the 1960s when it became established in

London London is the capital and largest city of England and the United Kingdom, with a population of just under 9 million. It stands on the River Thames in south-east England at the head of a estuary down to the North Sea, and has been a majo ...

, it arrived in

Paris Paris () is the capital and most populous city of France, with an estimated population of 2,165,423 residents in 2019 in an area of more than 105 km² (41 sq mi), making it the 30th most densely populated city in the world in 2020. S ...

by 1968 and had spread to Germany by 1989, where it has since been detected in many cities. The female insects have no wings and are therefore unable to fly, and their means of transportation is thought to be either with tree prunings, or on nursery stock. The nymphs at their crawler stage may be transported by wind and it is possible that they, or the eggs, are sometimes carried on the legs of birds. Scale insects can occur in both rural and urban environments, but town trees are usually less healthy and pest burdens tend to be higher in towns. This is thought to be due to various habitat differences in urban settings; higher temperatures, more air pollution, lower availability of nutrients, and more stress caused by lack of moisture (more run-off and less water penetrating the ground). ''P. regalis'' is primarily a pest of urban trees; its sap-sucking activities reduce its hosts' vigour, and the excess honeydew produced by the insects encourages the growth of

sooty mould Sooty mold (also spelled sooty mould) is a collective term for different Ascomycete fungi, which includes many genera, commonly ''Cladosporium'' and ''Alternaria''. It grows on plants and their fruit, but also environmental objects, like fences, ...

, which is unsightly.

Biology

The adult scale insect resembles a

limpet Limpets are a group of aquatic snails that exhibit a conical shell shape (patelliform) and a strong, muscular foot. Limpets are members of the class Gastropoda, but are polyphyletic, meaning the various groups called "limpets" descended indep ...

and remains stationary on the bark of its host tree where it feeds on

sap Sap is a fluid transported in xylem cells (vessel elements or tracheids) or phloem sieve tube elements of a plant. These cells transport water and nutrients throughout the plant. Sap is distinct from latex, resin, or cell sap; it is a separa ...

. Although males can occur, the insects are normally all female, and reproduce by

. In early summer, the mature female lays white, circular egg masses which become visible as they protrude slightly from under her brown scale. The eggs hatch into

nymphs A nymph ( grc, νύμφη, nýmphē, el, script=Latn, nímfi, label=Modern Greek; , ) in ancient Greek folklore is a minor female nature deity. Different from Greek goddesses, nymphs are generally regarded as personifications of nature, are typ ...

which crawl away from the mother along the branches to find foliage, where they start to suck sap. In the autumn, they return to the trunk and larger branches where they spend the winter as flat scales about long. They resume feeding in spring and are fully grown by early summer. There is a single generation each year and the adults die after reproducing. This insect has glands that produce several forms of wax; some glands produce water-repellent wax that keeps the air passages leading to the

spiracle Spiracle or spiraculum may refer to: * Spiracle (arthropods), opening in the exoskeletons of some arthropods * Spiracle (vertebrates), openings on the surface of some vertebrates * Spiraculum, a genus of land snails in family Cyclophoridae Cycl ...

s open. Other glands produce long white filaments of wax that serve a function in the construction of the sac that surrounds the eggs. To avoid getting contaminated by its own honeydew, the scale insect has a six-bristled mechanism close to the anus, with which it can flick away its excrement.

References

{{Taxonbar, from=Q10646659 Coccidae Insects described in 1968 Insect pests of ornamental plants Hemiptera of Asia