Bursaphelenchus
Encyclopedia
Bursaphelenchus is a genus
of nematode
s (roundworms) in the order
Aphelenchida
, containing about 100 described species
at present; new species are discovered frequently. Most are obligate mycophages, but some feed on wood
, with two species – the Red Ring Nematode (B. cocophilus) and the Pinewood Nematode (B. xylophilus) – economically significant as pests of the Coconut Palm (Cocos nucifera) and of pine
s (Pinus), respectively. Given that Bursaphelenchus species are usually hard to distinguish from one another except by trained helminthologists with access to microscope
s or DNA sequence
analysis, the entire genus is put under quarantine
in some countries. Where this is not the case however, these nematodes are becoming established as model organism
s for nematode developmental biology
, ecology
and genetics
.
s, with no hermaphrodite
s having been found in members of this genus, and only one species (B. okinawaensis) known to be parthenogenetic. These tiny worms inhabit soil
or decaying wood
, feeding on fungal
hyphen
s (e.g. of Grey Mould, Botrytis cinerea) or wood cells; while in the former case they may be beneficial by keeping down mould pathogens, in the latter case they may damage already-weakened trees to the point of death.
These nematodes are phoretic: their dauer larvae are dispersed between habitat
by insect
s, in particular bark beetle
s (Scolytidae), Lamiinae
long-horned beetles (e.g. sawyer beetles, Monochamus) or weevil
s (Curculionidae) in case of the wood-eating species, and soil-nesting bee
s in case of the fungivorous ones. The conditions under which dauer larvae are formed (and which thus e.g. in the case of B. xylophilus
trigger outbreaks of pine wilt disease) are not well understood in Bursaphelenchus but are known to differ from the situation in Caenorhabditis elegans
, the most important nematode model organism; hence the current research interest in the present genus. According to the initial research results, induction of dauer larvae formation in Bursaphelenchus is a far more complex process than in C. elegans and appears to be synchronized within populations, which explains the epidemic
outbreaks of disease caused by the plant pathogenic species of this genus.
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
of nematode
Nematode
The nematodes or roundworms are the most diverse phylum of pseudocoelomates, and one of the most diverse of all animals. Nematode species are very difficult to distinguish; over 28,000 have been described, of which over 16,000 are parasitic. It has been estimated that the total number of nematode...
s (roundworms) in the order
Order (biology)
In scientific classification used in biology, the order is# a taxonomic rank used in the classification of organisms. Other well-known ranks are life, domain, kingdom, phylum, class, family, genus, and species, with order fitting in between class and family...
Aphelenchida
Aphelenchida
A moderately large order of nematodes. Aphelenchida have a stylet for feeding and a very prominent median bulb in the oesophagus. They are cosmopolitan. Some are associated with insects, and may be ectoparasites or endoparasites, or merely use the insect as transport. Others are associated with...
, containing about 100 described species
Species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...
at present; new species are discovered frequently. Most are obligate mycophages, but some feed on wood
Wood
Wood is a hard, fibrous tissue found in many trees. It has been used for hundreds of thousands of years for both fuel and as a construction material. It is an organic material, a natural composite of cellulose fibers embedded in a matrix of lignin which resists compression...
, with two species – the Red Ring Nematode (B. cocophilus) and the Pinewood Nematode (B. xylophilus) – economically significant as pests of the Coconut Palm (Cocos nucifera) and of pine
Pine
Pines are trees in the genus Pinus ,in the family Pinaceae. They make up the monotypic subfamily Pinoideae. There are about 115 species of pine, although different authorities accept between 105 and 125 species.-Etymology:...
s (Pinus), respectively. Given that Bursaphelenchus species are usually hard to distinguish from one another except by trained helminthologists with access to microscope
Microscope
A microscope is an instrument used to see objects that are too small for the naked eye. The science of investigating small objects using such an instrument is called microscopy...
s or DNA sequence
DNA sequence
The sequence or primary structure of a nucleic acid is the composition of atoms that make up the nucleic acid and the chemical bonds that bond those atoms. Because nucleic acids, such as DNA and RNA, are unbranched polymers, this specification is equivalent to specifying the sequence of...
analysis, the entire genus is put under quarantine
Quarantine
Quarantine is compulsory isolation, typically to contain the spread of something considered dangerous, often but not always disease. The word comes from the Italian quarantena, meaning forty-day period....
in some countries. Where this is not the case however, these nematodes are becoming established as model organism
Model organism
A model organism is a non-human species that is extensively studied to understand particular biological phenomena, with the expectation that discoveries made in the organism model will provide insight into the workings of other organisms. Model organisms are in vivo models and are widely used to...
s for nematode developmental biology
Developmental biology
Developmental biology is the study of the process by which organisms grow and develop. Modern developmental biology studies the genetic control of cell growth, differentiation and "morphogenesis", which is the process that gives rise to tissues, organs and anatomy.- Related fields of study...
, ecology
Ecology
Ecology is the scientific study of the relations that living organisms have with respect to each other and their natural environment. Variables of interest to ecologists include the composition, distribution, amount , number, and changing states of organisms within and among ecosystems...
and genetics
Genetics
Genetics , a discipline of biology, is the science of genes, heredity, and variation in living organisms....
.
Ecology
Bursaphelenchus are generally bisexual nematodeNematode
The nematodes or roundworms are the most diverse phylum of pseudocoelomates, and one of the most diverse of all animals. Nematode species are very difficult to distinguish; over 28,000 have been described, of which over 16,000 are parasitic. It has been estimated that the total number of nematode...
s, with no hermaphrodite
Hermaphrodite
In biology, a hermaphrodite is an organism that has reproductive organs normally associated with both male and female sexes.Many taxonomic groups of animals do not have separate sexes. In these groups, hermaphroditism is a normal condition, enabling a form of sexual reproduction in which both...
s having been found in members of this genus, and only one species (B. okinawaensis) known to be parthenogenetic. These tiny worms inhabit soil
Soil
Soil is a natural body consisting of layers of mineral constituents of variable thicknesses, which differ from the parent materials in their morphological, physical, chemical, and mineralogical characteristics...
or decaying wood
Wood
Wood is a hard, fibrous tissue found in many trees. It has been used for hundreds of thousands of years for both fuel and as a construction material. It is an organic material, a natural composite of cellulose fibers embedded in a matrix of lignin which resists compression...
, feeding on fungal
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...
hyphen
Hyphen
The hyphen is a punctuation mark used to join words and to separate syllables of a single word. The use of hyphens is called hyphenation. The hyphen should not be confused with dashes , which are longer and have different uses, or with the minus sign which is also longer...
s (e.g. of Grey Mould, Botrytis cinerea) or wood cells; while in the former case they may be beneficial by keeping down mould pathogens, in the latter case they may damage already-weakened trees to the point of death.
These nematodes are phoretic: their dauer larvae are dispersed between habitat
Habitat
* Habitat , a place where a species lives and grows*Human habitat, a place where humans live, work or play** Space habitat, a space station intended as a permanent settlement...
by insect
Insect
Insects are a class of living creatures within the arthropods that have a chitinous exoskeleton, a three-part body , three pairs of jointed legs, compound eyes, and two antennae...
s, in particular bark beetle
Bark beetle
A bark beetle is one of approximately 220 genera with 6,000 species of beetles in the subfamily Scolytinae. Traditionally, this was considered a distinct family Scolytidae, but now it is understood that bark beetles are in fact very specialized members of the "true weevil" family...
s (Scolytidae), Lamiinae
Lamiinae
Lamiinae, commonly called flat-faced longhorns, are a subfamily of the longhorn beetle family . The subfamily includes over 750 genera, rivaled in diversity within the family only by the subfamily Cerambycinae.-Tribes:...
long-horned beetles (e.g. sawyer beetles, Monochamus) or weevil
Weevil
A weevil is any beetle from the Curculionoidea superfamily. They are usually small, less than , and herbivorous. There are over 60,000 species in several families, mostly in the family Curculionidae...
s (Curculionidae) in case of the wood-eating species, and soil-nesting bee
Bee
Bees are flying insects closely related to wasps and ants, and are known for their role in pollination and for producing honey and beeswax. Bees are a monophyletic lineage within the superfamily Apoidea, presently classified by the unranked taxon name Anthophila...
s in case of the fungivorous ones. The conditions under which dauer larvae are formed (and which thus e.g. in the case of B. xylophilus
Bursaphelenchus xylophilus
Bursaphelenchus xylophilus, commonly known as pine wood nematode or pine wilt nematode , is a nematode that infects pine trees and causes pine wilt...
trigger outbreaks of pine wilt disease) are not well understood in Bursaphelenchus but are known to differ from the situation in Caenorhabditis elegans
Caenorhabditis elegans
Caenorhabditis elegans is a free-living, transparent nematode , about 1 mm in length, which lives in temperate soil environments. Research into the molecular and developmental biology of C. elegans was begun in 1974 by Sydney Brenner and it has since been used extensively as a model...
, the most important nematode model organism; hence the current research interest in the present genus. According to the initial research results, induction of dauer larvae formation in Bursaphelenchus is a far more complex process than in C. elegans and appears to be synchronized within populations, which explains the epidemic
Epidemic
In epidemiology, an epidemic , occurs when new cases of a certain disease, in a given human population, and during a given period, substantially exceed what is expected based on recent experience...
outbreaks of disease caused by the plant pathogenic species of this genus.