Ambrosia beetle
Encyclopedia
Ambrosia beetles are beetles of the weevil
subfamilies Scolytinae and Platypodinae (Coleoptera, Curculionidae
), which live in nutritional symbiosis
with ambrosia fungi
and probably with bacteria
. The beetles excavate tunnels in dead trees in which they cultivate fungal gardens, their sole source of nutrition.
After landing on a suitable tree, an ambrosia beetle excavates a tunnel in which it releases spore
s of its fungal symbiont. The fungus penetrates the plant's xylem
tissue, digests it, and concentrates the nutrients on and near the surface of the beetle gallery. The majority of ambrosia beetles colonize xylem (sapwood and/or heartwood) of dying or recently dead trees. Species differ in their preference for different parts of trees, different stages of deterioration, in the shape of their tunnels (“galleries”). However, the majority of ambrosia beetles are not specialized to any taxonomic group of hosts, unlike most phytophagous organisms including the closely related bark beetle
s.
Until recently ambrosia beetles have been placed in independent families Scolytidae and Platypodidae, however, they are in fact some of the most highly derived weevils. There are about 3,000 known beetle species employing the ambrosia strategy.
Ambrosia beetles are an ecological guild, but not a phylogenetic clade. The ambrosia habit is an example of convergent evolution
, as several groups evolved the same symbiotic relationship independently. The highest diversity of ambrosia beetles is in the tropics. In the Paleotropical region, hundreds of species of Xyleborini
and Platypodinae are the main agent initiating dead wood decomposition. In the Neotropic
s, Platypodinae and Xyleborini
are joined by the scolytine tribe Cortylini. Compared to the diversity in the tropics, ambrosia beetle fauna in the temperate zone is rather limited. In the Nearctic
region it is dominated by a few species from Cortylini, Xyleborini and Xyloterini. In the Palearctic
ecozone
, significant groups are Xyloterini and Xyleborini, joined by Scolytoplatypodini in the Far East.
e graze on mycelium
exposed on the gallery walls and on bodies called sporodochia, clusters of the fungus’ spores. Most ambrosia beetle species don’t ingest the wood tissue; instead, the sawdust resulting from the excavation is pushed out of the gallery. Following the larval and pupal stage, adult ambrosia beetles collect masses of fungal spores into their mycangia
and leave the gallery to find their own tree.
A few dozen species of ambrosia fungi have been described, currently in the polyphyletic genera Ambrosiella
(mostly Microascales), Raffaelea, Ceratocystiopsis
and Dryadomyces (from Ophiostomatales), Ambrosiozyma (yeasts), and Entomocorticium (Basidiomycetes). Many more species remain to be discovered. Little is known about the bionomy or specificity of ambrosia fungi. Ambrosia fungi are thought to be dependent on transport and inoculation provided by their beetle symbionts, as they have not been found in any other habitat
. All ambrosia fungi are probably asexual
and clonal.. Some beetles are known to acquire ("steal") fungal inoculum from fungal gardens of other ambrosia beetle species
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...
subfamilies Scolytinae and Platypodinae (Coleoptera, Curculionidae
Curculionidae
Curculionidae is the family of the "true" weevils . It was formerly recognized in 1998 as the largest of any animal family, with over 40,000 species described worldwide at that time...
), which live in nutritional symbiosis
Symbiosis
Symbiosis is close and often long-term interaction between different biological species. In 1877 Bennett used the word symbiosis to describe the mutualistic relationship in lichens...
with ambrosia fungi
Ambrosia fungi
Ambrosia fungi are fungal symbionts of ambrosia beetles.There are a few dozen described ambrosia fungi, currently placed in polyphyletic genera Ambrosiella, Rafaellea and Dryadomyces . Probably many more species remain to be discovered...
and probably with bacteria
Bacteria
Bacteria are a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals...
. The beetles excavate tunnels in dead trees in which they cultivate fungal gardens, their sole source of nutrition.
After landing on a suitable tree, an ambrosia beetle excavates a tunnel in which it releases spore
Spore
In biology, a spore is a reproductive structure that is adapted for dispersal and surviving for extended periods of time in unfavorable conditions. Spores form part of the life cycles of many bacteria, plants, algae, fungi and some protozoa. According to scientist Dr...
s of its fungal symbiont. The fungus penetrates the plant's xylem
Xylem
Xylem is one of the two types of transport tissue in vascular plants. . The word xylem is derived from the Classical Greek word ξυλον , meaning "wood"; the best-known xylem tissue is wood, though it is found throughout the plant...
tissue, digests it, and concentrates the nutrients on and near the surface of the beetle gallery. The majority of ambrosia beetles colonize xylem (sapwood and/or heartwood) of dying or recently dead trees. Species differ in their preference for different parts of trees, different stages of deterioration, in the shape of their tunnels (“galleries”). However, the majority of ambrosia beetles are not specialized to any taxonomic group of hosts, unlike most phytophagous organisms including the closely related 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.
Classification and diversity
Ambrosia beetles are an ecological guild, but not a phylogenetic clade. The ambrosia habit is an example of convergent evolution
Convergent evolution
Convergent evolution describes the acquisition of the same biological trait in unrelated lineages.The wing is a classic example of convergent evolution in action. Although their last common ancestor did not have wings, both birds and bats do, and are capable of powered flight. The wings are...
, as several groups evolved the same symbiotic relationship independently. The highest diversity of ambrosia beetles is in the tropics. In the Paleotropical region, hundreds of species of Xyleborini
Xyleborini
Xyleborini are a tribe of bark beetles , highly specialized weevils of the subfamily Scolytinae. Much of the ambrosia beetle fauna in Eurasia and the Americas consists of Xyleborini species. Some Xyleborini are notorious invasive species.Most genera are small or even monotypic, and contain 1-8...
and Platypodinae are the main agent initiating dead wood decomposition. In the Neotropic
Neotropic
In biogeography, the Neotropic or Neotropical zone is one of the eight terrestrial ecozones. This ecozone includes South and Central America, the Mexican lowlands, the Caribbean islands, and southern Florida, because these regions share a large number of plant and animal groups.It is sometimes used...
s, Platypodinae and Xyleborini
Xyleborini
Xyleborini are a tribe of bark beetles , highly specialized weevils of the subfamily Scolytinae. Much of the ambrosia beetle fauna in Eurasia and the Americas consists of Xyleborini species. Some Xyleborini are notorious invasive species.Most genera are small or even monotypic, and contain 1-8...
are joined by the scolytine tribe Cortylini. Compared to the diversity in the tropics, ambrosia beetle fauna in the temperate zone is rather limited. In the Nearctic
Nearctic
The Nearctic is one of the eight terrestrial ecozones dividing the Earth's land surface.The Nearctic ecozone covers most of North America, including Greenland and the highlands of Mexico...
region it is dominated by a few species from Cortylini, Xyleborini and Xyloterini. In the Palearctic
Palearctic
The Palearctic or Palaearctic is one of the eight ecozones dividing the Earth's surface.Physically, the Palearctic is the largest ecozone...
ecozone
Ecozone
An ecozone is the broadest biogeographic division of the Earth's land surface, based on distributional patterns of terrestrial organisms.Ecozones delineate large areas of the Earth's surface within which organisms have been evolving in relative isolation over long periods of time, separated from...
, significant groups are Xyloterini and Xyleborini, joined by Scolytoplatypodini in the Far East.
The symbiotic relationship
Beetles and their larvaLarva
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...
e graze on mycelium
Mycelium
thumb|right|Fungal myceliaMycelium is the vegetative part of a fungus, consisting of a mass of branching, thread-like hyphae. The mass of hyphae is sometimes called shiro, especially within the fairy ring fungi. Fungal colonies composed of mycelia are found in soil and on or within many other...
exposed on the gallery walls and on bodies called sporodochia, clusters of the fungus’ spores. Most ambrosia beetle species don’t ingest the wood tissue; instead, the sawdust resulting from the excavation is pushed out of the gallery. Following the larval and pupal stage, adult ambrosia beetles collect masses of fungal spores into their mycangia
Mycangium
The term mycangium is used in biology for special structures on the body of an animal that are adapted for the transport of symbiotic fungi . This is seen in many xylophagous insects , which apparently derive much of their nutrition from the digestion of various fungi that are growing amidst the...
and leave the gallery to find their own tree.
A few dozen species of ambrosia fungi have been described, currently in the polyphyletic genera Ambrosiella
Ambrosiella
Ambrosiella is a genus of fungi within the Ceratocystidaceae family.-Species:*Ambrosiella beaveri*Ambrosiella brunnea*Ambrosiella clodiensis*Ambrosiella ferruginea*Ambrosiella gnathotrichi*Ambrosiella hartigii...
(mostly Microascales), Raffaelea, Ceratocystiopsis
Ceratocystiopsis
Ceratocystiopsis is a genus of fungi within the Ophiostomataceae family.-External links:* at Index Fungorum...
and Dryadomyces (from Ophiostomatales), Ambrosiozyma (yeasts), and Entomocorticium (Basidiomycetes). Many more species remain to be discovered. Little is known about the bionomy or specificity of ambrosia fungi. Ambrosia fungi are thought to be dependent on transport and inoculation provided by their beetle symbionts, as they have not been found in any other 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...
. All ambrosia fungi are probably asexual
Asexual reproduction
Asexual reproduction is a mode of reproduction by which offspring arise from a single parent, and inherit the genes of that parent only, it is reproduction which does not involve meiosis, ploidy reduction, or fertilization. A more stringent definition is agamogenesis which is reproduction without...
and clonal.. Some beetles are known to acquire ("steal") fungal inoculum from fungal gardens of other ambrosia beetle species
Evolutionary origin
During their evolution, most scolytid and platypodid weevils became progressively more or less dependent on fungi regularly co-habiting dead trees. This evolution had various outcomes in different groups:- Some phloemPhloemIn vascular plants, phloem is the living tissue that carries organic nutrients , in particular, glucose, a sugar, to all parts of the plant where needed. In trees, the phloem is the innermost layer of the bark, hence the name, derived from the Greek word "bark"...
-eating bark beetles (phloeophages) are probably employing aggressive phytopathogenic fungal associates to kill live trees. - Many of phloem-feeding bark beetles use phloem-infesting fungi as an addition to their diet. Some phloeophages became more or less dependent on such a mixed diet and evolved mycangiaMycangiumThe term mycangium is used in biology for special structures on the body of an animal that are adapted for the transport of symbiotic fungi . This is seen in many xylophagous insects , which apparently derive much of their nutrition from the digestion of various fungi that are growing amidst the...
to transport their symbionts from maternal trees to newly infested trees. These beetles are called mycophloeophages. - Ambrosia beetles and ambrosia fungi are thus only one end of the spectrum of the weevil-fungus association, where both the beetle and the fungus became completely dependent on each other.
External links
- Images and info on the Ambrosia Symbiosis at North Carolina State University.
- The MSU HISL database contains a worldwide species list of Xyleborini, a major group of ambrosia beetles, from the Catalog of Scolytidae and Platypodidae of S.L. Wood and D.E. Bright (1992)]
- A USDA-sponsored information resource and key to the world genera of Xyleborini
- American Bark and Ambrosia Beetles
- More information on ambrosia beetle social behaviour and fungiculture on http://behav.zoology.unibe.ch/index.php?pp=55&p=46
- Farewell to taco topping? The effects of the Redbay ambrosia beetle and laurel wilt disease
- Ambrosia beetles on the UFUniversity of FloridaThe University of Florida is an American public land-grant, sea-grant, and space-grant research university located on a campus in Gainesville, Florida. The university traces its historical origins to 1853, and has operated continuously on its present Gainesville campus since September 1906...
/ IFASInstitute of Food and Agricultural SciencesThe University of Florida’s Institute of Food and Agricultural Sciences is a federal-state-county partnership dedicated to developing knowledge in agriculture, human and natural resources, and the life sciences, and enhancing and sustaining the quality of human life by making that information...
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