Cryptococcus fagisuga
Encyclopedia
Cryptococcus fagisuga, commonly known as the beech scale or woolly beech scale, is a felted scale insect
in the superfamily
Coccoidea that infests beech trees of the genus Fagus
. It is associated with the transmission of beech bark disease
because the puncture holes it makes in the bark
allow entry of pathogen
ic fungi
which have been identified as Nectria coccinea
var. faginata and sometimes Nectria galligena.
since before 1849. Until 1914 it was thought that the beech scale insect itself was responsible for the disease. Subsequently it was discovered that a fungus, then identified as Nectria ditissima, was in fact killing the trees infested by the scale. Around 1890 the scale insect was accidentally introduced into Nova Scotia
. By 1932, the scale and its associated Nectria fungus had spread to many areas of the Maritime Provinces
and parts of eastern and south central Maine
. It continues to spread in North America and is now found in Quebec
, New England
, New York
, New Jersey
, Pennsylvania
and West Virginia
. Attempts are being made to discover the geographic origin of beech scale in order to try to identify any natural enemies that might hold promise for its biological control
. From these studies and associated ribosomal DNA
analysis, it seems likely that the pest originated in the region of northeast Greece, northern Iran, the Caucasus and the Black Sea drainage basin on the host beech subspecies F. sylvatica orientalis.
There are no male beech scale insects and the females reproduce by parthogenesis. From midsummer onwards, they deposit four to eight pale yellow eggs, attached to each other in strings end to end, on the bark of the trees where they have been feeding. The wingless larvae that hatch out about twenty days later are known as crawlers or nymphs
. They have well-developed legs and short antennae. Some remain concealed under the female, which dies after the eggs are laid, and others disperse to cracks and crevices on the tree. A few get washed down or fall to the ground and most of these perish. Occasionally one may find its way to another beech tree, perhaps wafted there by the wind or on the foot of a bird, and founds a new colony. Having found a location on a suitable tree, the crawler forces its tubular stylet into the bark and starts to feed. At this stage, it moult
s and becomes a second-stage, legless nymph, and will remain sedentary for the rest of its life. It secretes wax from glands and is soon covered in a protective coating of wool-like material. After overwintering it completes a second moult in the spring to become a mature female.
tissue of the bark. The small wounds produced when it feeds allow the Nectria fungi to invade infested trees. The insect colonises beech trees that are aged at least thirty years. Studies have shown that younger trees produce defensive chemicals which deter infestation. A ladybird beetle Chilocorus stigma feeds on this scale and is common throughout most of the Eastern United States, but this predator
does not reduce scale populations sufficiently to control infestations. Persistent severely cold weather may kill beech scale and air temperatures of -37°C have been shown to be lethal to insects not protected by snow. Although trees are weakened when supporting scale colonies, this does not usually cause mortality, which only occurs after the trees have been invaded by the Nectria fungi. It usually takes three to six years of infestation by the scale insect before the fungus reaches critical levels. Where beech bark disease becomes established, most of the larger trees will die. Some trees seem to be partially resistant to the disease and a small number seem to be completely resistant. This may be partly due to the fact that trees with smooth bark provide fewer cracks and crevices in which the scale insect can flourish.
Scale insect
The scale insects are small insects of the order Hemiptera, generally classified as the superfamily Coccoidea. There are about 8,000 species of scale insects.-Ecology:...
in the superfamily
Taxonomic rank
In biological classification, rank is the level in a taxonomic hierarchy. Examples of taxonomic ranks are species, genus, family, and class. Each rank subsumes under it a number of less general categories...
Coccoidea that infests beech trees of the genus Fagus
Beech
Beech is a genus of ten species of deciduous trees in the family Fagaceae, native to temperate Europe, Asia and North America.-Habit:...
. It is associated with the transmission of beech bark disease
Beech Bark Disease
Beech bark disease is a disease that causes mortality and defects in beech trees in the eastern United States and Europe. In North America, the disease results when the beech scale insect, Cryptococcus fagisuga, attacks the bark, creating a wound. Later, two different fungi Beech bark disease is a...
because the puncture holes it makes in the bark
Bark
Bark is the outermost layers of stems and roots of woody plants. Plants with bark include trees, woody vines and shrubs. Bark refers to all the tissues outside of the vascular cambium and is a nontechnical term. It overlays the wood and consists of the inner bark and the outer bark. The inner...
allow entry of pathogen
Pathogen
A pathogen gignomai "I give birth to") or infectious agent — colloquially, a germ — is a microbe or microorganism such as a virus, bacterium, prion, or fungus that causes disease in its animal or plant host...
ic fungi
Fungus
A fungus is a member of a large group of eukaryotic organisms that includes microorganisms such as yeasts and molds , as well as the more familiar mushrooms. These organisms are classified as a kingdom, Fungi, which is separate from plants, animals, and bacteria...
which have been identified as Nectria coccinea
Nectria coccinea
Nectria coccinea is a fungal plant pathogen. The variant Nectria coccinea var. faginata causes beech bark disease, and can infect the tree via the feeding holes made by the beech scale insect Cryptococcus fagisuga.- External links :* *...
var. faginata and sometimes Nectria galligena.
History and distribution
Beech bark disease has been recorded as affecting common beech trees, Fagus sylvatica, in EuropeEurope
Europe is, by convention, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally 'divided' from Asia to its east by the watershed divides of the Ural and Caucasus Mountains, the Ural River, the Caspian and Black Seas, and the waterways connecting...
since before 1849. Until 1914 it was thought that the beech scale insect itself was responsible for the disease. Subsequently it was discovered that a fungus, then identified as Nectria ditissima, was in fact killing the trees infested by the scale. Around 1890 the scale insect was accidentally introduced into Nova Scotia
Nova Scotia
Nova Scotia is one of Canada's three Maritime provinces and is the most populous province in Atlantic Canada. The name of the province is Latin for "New Scotland," but "Nova Scotia" is the recognized, English-language name of the province. The provincial capital is Halifax. Nova Scotia is the...
. By 1932, the scale and its associated Nectria fungus had spread to many areas of the Maritime Provinces
Maritimes
The Maritime provinces, also called the Maritimes or the Canadian Maritimes, is a region of Eastern Canada consisting of three provinces, New Brunswick, Nova Scotia, and Prince Edward Island. On the Atlantic coast, the Maritimes are a subregion of Atlantic Canada, which also includes the...
and parts of eastern and south central Maine
Maine
Maine is a state in the New England region of the northeastern United States, bordered by the Atlantic Ocean to the east and south, New Hampshire to the west, and the Canadian provinces of Quebec to the northwest and New Brunswick to the northeast. Maine is both the northernmost and easternmost...
. It continues to spread in North America and is now found in Quebec
Quebec
Quebec or is a province in east-central Canada. It is the only Canadian province with a predominantly French-speaking population and the only one whose sole official language is French at the provincial level....
, New England
New England
New England is a region in the northeastern corner of the United States consisting of the six states of Maine, New Hampshire, Vermont, Massachusetts, Rhode Island, and Connecticut...
, New York
New York
New York is a state in the Northeastern region of the United States. It is the nation's third most populous state. New York is bordered by New Jersey and Pennsylvania to the south, and by Connecticut, Massachusetts and Vermont to the east...
, New Jersey
New Jersey
New Jersey is a state in the Northeastern and Middle Atlantic regions of the United States. , its population was 8,791,894. It is bordered on the north and east by the state of New York, on the southeast and south by the Atlantic Ocean, on the west by Pennsylvania and on the southwest by Delaware...
, Pennsylvania
Pennsylvania
The Commonwealth of Pennsylvania is a U.S. state that is located in the Northeastern and Mid-Atlantic regions of the United States. The state borders Delaware and Maryland to the south, West Virginia to the southwest, Ohio to the west, New York and Ontario, Canada, to the north, and New Jersey to...
and West Virginia
West Virginia
West Virginia is a state in the Appalachian and Southeastern regions of the United States, bordered by Virginia to the southeast, Kentucky to the southwest, Ohio to the northwest, Pennsylvania to the northeast and Maryland to the east...
. Attempts are being made to discover the geographic origin of beech scale in order to try to identify any natural enemies that might hold promise for its biological control
Biological pest control
Biological control of pests in agriculture is a method of controlling pests that relies on predation, parasitism, herbivory, or other natural mechanisms...
. From these studies and associated ribosomal DNA
Ribosomal DNA
Ribosomal DNA codes for ribosomal RNA. The ribosome is an intracellular macromolecule that produces proteins or polypeptide chains. The ribosome itself consists of a composite of proteins and RNA. As shown in the figure, rDNA consists of a tandem repeat of a unit segment, an operon, composed of...
analysis, it seems likely that the pest originated in the region of northeast Greece, northern Iran, the Caucasus and the Black Sea drainage basin on the host beech subspecies F. sylvatica orientalis.
Description
Adult scales are elliptical and about one millimetre long and are covered by a cream coloured, cottony wax secretion. They have reddish-brown eyes, no wings, rudimentary antennae and legs, and numerous minute wax-secreting glands. The stylet through which they suck sap can be up to two millimetres long.Life cycle
Nymph (biology)
In biology, a nymph is the immature form of some invertebrates, particularly insects, which undergoes gradual metamorphosis before reaching its adult stage. Unlike a typical larva, a nymph's overall form already resembles that of the adult. In addition, while a nymph moults it never enters a...
. They have well-developed legs and short antennae. Some remain concealed under the female, which dies after the eggs are laid, and others disperse to cracks and crevices on the tree. A few get washed down or fall to the ground and most of these perish. Occasionally one may find its way to another beech tree, perhaps wafted there by the wind or on the foot of a bird, and founds a new colony. Having found a location on a suitable tree, the crawler forces its tubular stylet into the bark and starts to feed. At this stage, it moult
Moult
In biology, moulting or molting , also known as sloughing, shedding, or for some species, ecdysis, is the manner in which an animal routinely casts off a part of its body , either at specific times of year, or at specific points in its life cycle.Moulting can involve the epidermis , pelage...
s and becomes a second-stage, legless nymph, and will remain sedentary for the rest of its life. It secretes wax from glands and is soon covered in a protective coating of wool-like material. After overwintering it completes a second moult in the spring to become a mature female.
Biology
The beech scale is monophagous, being found only on beech trees, and sucks sap from the parenchymeParenchyma
Parenchyma is a term used to describe a bulk of a substance. It is used in different ways in animals and in plants.The term is New Latin, f. Greek παρέγχυμα - parenkhuma, "visceral flesh", f. παρεγχεῖν - parenkhein, "to pour in" f. para-, "beside" + en-, "in" + khein, "to pour"...
tissue of the bark. The small wounds produced when it feeds allow the Nectria fungi to invade infested trees. The insect colonises beech trees that are aged at least thirty years. Studies have shown that younger trees produce defensive chemicals which deter infestation. A ladybird beetle Chilocorus stigma feeds on this scale and is common throughout most of the Eastern United States, but this predator
Predation
In ecology, predation describes a biological interaction where a predator feeds on its prey . Predators may or may not kill their prey prior to feeding on them, but the act of predation always results in the death of its prey and the eventual absorption of the prey's tissue through consumption...
does not reduce scale populations sufficiently to control infestations. Persistent severely cold weather may kill beech scale and air temperatures of -37°C have been shown to be lethal to insects not protected by snow. Although trees are weakened when supporting scale colonies, this does not usually cause mortality, which only occurs after the trees have been invaded by the Nectria fungi. It usually takes three to six years of infestation by the scale insect before the fungus reaches critical levels. Where beech bark disease becomes established, most of the larger trees will die. Some trees seem to be partially resistant to the disease and a small number seem to be completely resistant. This may be partly due to the fact that trees with smooth bark provide fewer cracks and crevices in which the scale insect can flourish.