Phytobia betulae

Phytobia betulae
Scientific classification
Kingdom:	Animalia
Phylum:	Arthropoda
Class:	Insecta
Order:	Diptera
Subsection:	Acalyptratae
Superfamily:	Opomyzoidea
Family:	Agromyzidae
Subfamily:	Phytomyzinae
Genus:	Phytobia
Species:	P. betulae
Binomial name
	Phytobia betulae; (Kangas, 1935) [1]

Last updated July 23, 2019

Phytobia betulae is a species of fly in the family Agromyzidae. It is native to Northern and Eastern Europe, being common in Scandinavia. Its larvae tunnel through the branches and trunk of birch trees, often leaving a dark stain in the timber but not adversely affecting the tree's growth.

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 sexes or mating types can produce fertile offspring, typically by sexual reproduction. Other ways of defining species include their karyotype, DNA sequence, morphology, behaviour or ecological niche. In addition, paleontologists use the concept of the chronospecies since fossil reproduction cannot be examined.

Flies are insects with a pair of functional wings for flight and a pair of specialized hindwings called halteres for balance. They are classified as an order called Diptera, that name being derived from the Greek δι- di- "two", and πτερόν pteron "wings". The order Diptera is divided into two suborders, with about 110 families divided between them; the families contain an estimated 1,000,000 species, including the familiar housefly, horse-fly, crane fly, and hoverfly; although only about 125,000 species have a species description published. The earliest fly fossils found so far are from the Triassic, about 240 million years ago; phylogenetic analysis suggests that flies originated in the Permian, about 260 million years ago.

The Agromyzidae are a family commonly referred to as the leaf-miner flies, for the feeding habits of their larvae, most of which are leaf miners on various plants.

Description

The eggs of P. betulae are small, white, and oval. The larvae are transparent or white and narrowly cylindrical, with the final (third) instar reaching a length of 15 to 20 mm (0.6 to 0.8 in). The pupae are barrel-shaped, whitish, or pale yellow. The adults are small black flies, up to 5 mm (0.2 in) long.^[2]

The egg is the organic vessel containing the zygote in which an embryo develops until it can survive on its own; at which point the animal hatches. An egg results from fertilization of an egg cell. Most arthropods, vertebrates, and mollusks lay eggs, although some, such as scorpions do not.

A larva is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle.

An instar is a developmental stage of arthropods, such as insects, between each moult (ecdysis), until sexual maturity is reached. Arthropods must shed the exoskeleton in order to grow or assume a new form. Differences between instars can often be seen in altered body proportions, colors, patterns, changes in the number of body segments or head width. After moulting, i.e. shedding their exoskeleton, the juvenile arthropods continue in their life cycle until they either pupate or moult again. The instar period of growth is fixed; however, in some insects, like the salvinia stem-borer moth, the number of instars depends on early larval nutrition. Some arthropods can continue to moult after sexual maturity, but the stages between these subsequent moults are generally not called instars.

Life cycle

P. betulae has a single generation each year. The insects emerge from pupation in early summer and the female searches out a suitable host tree, usually Betula pendula or B. pubescens . Eggs are deposited singly under the bark of new-growth twigs. They hatch after about one week and the larvae tunnel downwards along the shoot within the differentiating xylem layer. Although narrow at first, the tunnels become up to 4 mm (0.16 in) wide and extremely long (17 m (56 ft)), often reaching the base of the tree; the larvae may reverse direction and mine upwards in the trunk or continue to tunnel into the root system before returning to the trunk.^[2] Larval tunnels from this species will often cause discoloration (brown stripes) in the wood of birch trees, but they do not however affect the tree's survival and growth.^[3] The tunnels are filled with frass, and there may be some short side passages in the tree bole. The larvae emerge near the base of the tree in the late summer or early autumn, fall to the ground and pupate in the plant litter or soil, where they overwinter.^[2]

A pupa is the life stage of some insects undergoing transformation between immature and mature stages. The pupal stage is found only in holometabolous insects, those that undergo a complete metamorphosis, with four life stages: egg, larva, pupa, and imago. The processes of entering and completing the pupal stage are controlled by the insect's hormones, especially juvenile hormone, prothoracicotropic hormone, and ecdysone.

In biology and medicine, a host is an organism that harbours a parasitic, a mutualistic, or a commensalist guest (symbiont), the guest typically being provided with nourishment and shelter. Examples include animals playing host to parasitic worms, cells harbouring pathogenic (disease-causing) viruses, a bean plant hosting mutualistic (helpful) nitrogen-fixing bacteria. More specifically in botany, a host plant supplies food resources to micropredators, which have an evolutionarily stable relationship with their hosts similar to ectoparasitism. The host range is the collection of hosts that an organism can use as a partner.

Betula pendula, commonly known as silver birch, warty birch, European white birch, or East Asian white birch, is a species of tree in the family Betulaceae, native to Europe and parts of Asia, though in southern Europe, it is only found at higher altitudes. Its range extends into Siberia, China, and southwest Asia in the mountains of northern Turkey, the Caucasus, and northern Iran. It has been introduced into North America, where it is known as the European white birch, and is considered invasive in some states in the United States and parts of Canada. The tree can also be found in more temperate regions of Australia.

Ecology

When choosing where to lay eggs, the adult female P. betulae probes twigs in the upper part of the crown of host trees with its ovipositor and tends to select vigorous young shoots. The larvae do best on fast growing trees and the tree may be infected every year, leaving permanent marks in the timber. Once the tree reaches around thirty years of age its growth rate slows and infections diminish. Two species of braconid and one species of ichneumid wasp parasitize the larvae, laying their eggs in the first instar. The pupae are probably eaten by predatory insects and small mammals and birds.^[2]

The crown of a plant refers to the totality of an individual plant's aboveground parts, including stems, leaves, and reproductive structures. A plant community canopy consists of one or more plant crowns growing in a given area.

Ovipositor Anatomical structure for laying eggs

The ovipositor is an organ used by some animals for the laying of eggs. In insects, an ovipositor consists of a maximum of three pairs of appendages. The details and morphology of the ovipositor vary, but typically its form is adapted to functions such as transmitting the egg, preparing a place for it, and placing it properly. For insects, the organ is used merely to attach the egg to some surface, but for many parasitic species, it is a piercing organ as well.

The Braconidae are a family of parasitoid wasps. After the closely related Ichneumonidae, braconids make up the second-largest family in the order Hymenoptera, with about 17,000 recognized species and many thousands more undescribed. One analysis estimated a total between 30,000 and 50,000, and another provided a narrower estimate between 42,000 and 43,000 species.

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References

↑ "Phytobia betulae (Kangas, 1935)". Taxon profile. BioLib. Retrieved 1 June 2019.
1 2 3 4 Lieutier, François; Day, Keith R.; Battisti, Andrea; Grégoire, Jean-Claude; Evans, Hugh F. (2007). Bark and Wood Boring Insects in Living Trees in Europe, a Synthesis. Springer Science & Business Media. pp. 534–537. ISBN 978-1-4020-2241-8.
↑ Housi, Matti; Roininen, Heikki; Saranpää, Pekka; Ylioja, Tiina (1998). "Larval Tunnels of Phytobia betulae (Diptera: Agromyzidae) in Birch Wood". Journal of Economic Entomology. 91 (1): 175–181. doi:10.1093/jee/91.1.175. ISSN 0022-0493.

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[1] "Phytobia betulae (Kangas, 1935)". Taxon profile. BioLib. Retrieved 1 June 2019.

[Lieutier-2] 1 2 3 4 Lieutier, François; Day, Keith R.; Battisti, Andrea; Grégoire, Jean-Claude; Evans, Hugh F. (2007). Bark and Wood Boring Insects in Living Trees in Europe, a Synthesis. Springer Science & Business Media. pp. 534–537. ISBN 978-1-4020-2241-8.

[:0-3] Housi, Matti; Roininen, Heikki; Saranpää, Pekka; Ylioja, Tiina (1998). "Larval Tunnels of Phytobia betulae (Diptera: Agromyzidae) in Birch Wood". Journal of Economic Entomology. 91 (1): 175–181. doi:10.1093/jee/91.1.175. ISSN 0022-0493.