Ambrosia beetle

Ambrosia beetles are beetles of the weevil subfamilies Scolytinae and Platypodinae (Coleoptera, Curculionidae), which live in nutritional symbiosis with ambrosia fungi. The beetles excavate tunnels in dead or stressed 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 spores of its fungal symbiont. The fungus penetrates the plant's xylem tissue, extracts nutrients from it, and concentrates the nutrients on and near the surface of the beetle gallery. Ambrosia fungi are typically poor wood degraders, and instead utilize less demanding nutrients.[1] The majority of ambrosia beetles colonize xylem (sapwood and/or heartwood) of recently dead trees, but some attack stressed trees that are still alive, and a few species attack healthy trees.[2] Species differ in their preference for different parts of trees, different stages of deterioration, and 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 beetles. One species of ambrosia beetle, Austroplatypus incompertus exhibits eusociality, one of the few organisms outside of Hymenoptera and Isoptera to do so.

Classification and diversity

Xylosandrus crassiusculus galleryR
Gallery of Xylosandrus crassiusculus split open, with pupae and black fungus

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.[3] There are about 3,000 known beetle species employing the ambrosia strategy.[4]

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.[5] 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 Neotropics, 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.

Dinoplatypus chevrolati
Dinoplatypus chevrolati from Papua New Guinea, an example of Platypodinae, another species-rich group of ambrosia beetles

The symbiotic relationship

Beetles and their larvae 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 (Basidiomycota). 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.[6] Some beetles are known to acquire ("steal") fungal inoculum from fungal gardens of other ambrosia beetle species.[7]

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 phloem-eating bark beetles (phloeophages) are vectors of phytopathogenic fungi, which in some cases contribute to tree death.[8] The extent to which fungal pathogenicity benefits the beetles themselves is not at all trivial and remains disputed.[9]
  • Many of phloem-feeding bark beetles use phloem-infesting fungi as an addition to their diet. Some phloeophages became dependent on such a mixed diet and evolved mycangia to transport their symbionts from maternal trees to newly infested trees.[10] 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.[11]

Impact on forests

The vast majority of ambrosia beetles colonize dead trees, and have minor or no economic effect. A few species are able to colonize living stressed trees (Xylosandrus).[12] A few species are able to attack live and healthy trees, and those can reach epidemic proportions in non-native, invaded regions (Xyleborus glabratus, Euwallacea fornicatus[13]).

Beetle species that readily colonize lumber, such as sawlogs, green lumber, and stave-bolts, often cause region-specific economic loss from the pinhole and stained-wood defects caused by their brood galleries. In Northern USA and Canada, conifer logs are attractive to Trypodendron lineatum (Oliv.) during the spring swarming flight (Dyer 1967).[14] Previous studies showed that short log sections become attractive more rapidly than corresponding long logs.

See also

References

  1. ^ Kasson, M.T., Wickert, K.L., Stauder, C.M., Macias, A.M., Berger, M.C., Simmons, D.R., Short, D.P., DeVallance, D.B. and Hulcr, J., 2016. Mutualism with aggressive wood-degrading Flavodon ambrosius (Polyporales) facilitates niche expansion and communal social structure in Ambrosiophilus ambrosia beetles. Fungal Ecology, 23, pp.86-96.
  2. ^ Hulcr, J. and Stelinski, L.L., 2017. The ambrosia symbiosis: From evolutionary ecology to practical management. Annual Review of Entomology, 62, pp.285-303.
  3. ^ Kuschel, G., R. A. B. Leschen, et al. (2000): Platypodidae under scrutiny. Invertebrate Taxonomy 14: 771-805.
    Marvaldi, A. E., A. S. Sequeira, et al. (2002): Molecular and Morphological Phylogenetics of Weevils (Coleoptera, Curculionoidea): Do Niche Shifts Accompany Diversifcation? Systematic Biology 51(5): 761-785.
    Duane D. McKenna, Andrea S. Sequeira, Adriana E. Marvaldi, and Brian D. Farrell. 2009. Temporal lags and overlap in the diversification of weevil and flowering plant. PNAS 106:7083-7088.
  4. ^ Hulcr, J., Atkinson, T.H., Cognato, A.I., Jordal, B.H. and McKenna, D.D., 2015. Morphology, taxonomy, and phylogenetics of bark beetles. Bark beetles: biology and ecology of native and invasive species, pp.41-84.
  5. ^ Farrell, B. D., A. S. O. Sequeira, et al. (2001): The evolution of agriculture in beetles (Curculionidae: Scolytinae and Platypodinae). Evolution 55: 2011-2027.
  6. ^ Malloch, D., and M. Blackwell. 1993. Dispersal biology of ophiostomatoid fungi. p. 195-206. In: Ceratocystis and Ophiostoma: Taxonomy, Ecology and Pathology. Eds., Wingfield, M.J., K.A. Seifert, and J.F. Webber. APS, St. Paul.
  7. ^ Hulcr, J., Cognato, A. I. 2010. Repeated evolution of theft in fungus farming ambrosia beetles. Evolution, 64 (11): 3205-3212
  8. ^ Paine, T. D., K. F. Raffa, et al. (1997): Interactions between scolytid bark beetles, their associated fungi and live host conifers. Annual Review of Entomology 42: 179-206.
  9. ^ Six, D.L. and Wingfield, M.J., 2011. The role of phytopathogenicity in bark beetle–fungus symbioses: a challenge to the classic paradigm. Annual Review of Entomology, 56, pp.255-272.
  10. ^ Klepzik, K. D. and D. L. Six (2004): Bark Beetle – Fungal Symbiosis: Context Dependency in Complex Associations. Symbiosis 37: 189-205.
  11. ^ Beaver, R. A. (1989): Insect-Fungus Relationship in the Bark and Ambrosia Beetles. Insect-Fungus Interactions. N. Wilding, N. M. Collins, P. M. Hammond and J. F. Webber, Academic Press: 121-143.
  12. ^ Ranger, C.M., Reding, M.E., Persad, A.B. and Herms, D.A., 2010. Ability of stress‐related volatiles to attract and induce attacks by Xylosandrus germanus and other ambrosia beetles. Agricultural and Forest Entomology, 12(2), pp.177-185.
  13. ^ Hulcr, J., Black, A., Prior, K., Chen, C.Y. and Li, H.F., 2017. Studies of ambrosia beetles (Coleoptera: Curculionidae) in their native ranges help predict invasion impact. Florida Entomologist, 100(2), pp.257-261.
  14. ^ Dyer, E.D.A. 1967. Relation of attack by ambrosia beetle (Trypodendron lineatum (Oliv.)) to felling date of spruce in central British Columbia. For. Can., Can. For. Serv., Ottawa ON, Bi-mo. Res. Notes 23(2):11.

External links

Bibliography

Ambrosia fungi

Ambrosia fungi are fungal symbionts of ambrosia beetles including the polyphagous and Kuroshio shot hole borers.There are a few dozen species described ambrosia fungi, currently placed in polyphyletic genera Ambrosiella, Rafaellea and Dryadomyces (all from Ophiostomatales, Ascomycetes). Probably many more species remain to be discovered. Little is known about ecology of ambrosia fungi, as well as about their specificity to ambrosia beetle species. 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.

Austroplatypus incompertus

Austroplatypus incompertus is a species of ambrosia beetle belonging to the weevil family, native to Australia, with a verified distribution in New South Wales and Victoria. It forms colonies in the heartwood of Eucalyptus trees and is the first beetle to be recognized as a eusocial insect. Austroplatypus incompertus is considered eusocial because groups contain a single fertilized female that is protected and taken care of by a small number of unfertilized females that also do much of the work. These beetles appear to be the oldest farming creatures, having domesticated fungi nearly 90 million years ago. The species likely passed on cultivated fungi to other weevils.

Laurel wilt

Laurel wilt, also called laurel wilt disease, is a vascular disease caused by the fungus Raffaelea lauricola, which is transmitted by the invasive redbay ambrosia beetle, Xyleborus glabratus. The disease affects and kills members of the laurel family. The avocado is perhaps the most commercially valuable plant affected by laurel wilt.

Platypus australis

Platypus australis, commonly known as the polyphagous pinhole borer, is a species of ambrosia beetle in the weevil family Curculionidae found in Australia. It only eats superficial layers of wood, hence the damage is trivial.

Platypus cylindrus

Platypus cylindrus, commonly known as the oak pinhole borer, is a species of ambrosia beetle in the weevil family Curculionidae. The adults and larvae burrow under the bark of mature oak trees. It is native to Europe.

Platypus quercivorus

Platypus quercivorus, the oak ambrosia beetle, is a species of weevil and pest of broad-leaved trees. This species is most commonly known for vectoring the fungus responsible for excessive oak dieback in Japan since the 1980s. It is found in Japan, India, Indonesia, New Guinea, and Taiwan.

Raffaelea

Raffaelea is a genus of ambrosia fungi in the family Ophiostomataceae. It was cirumscribed by mycologists Josef Adolph von Arx and Grégoire L. Hennebert in 1965 with Raffaelea ambrosiae as the type species.Laurel wilt is a disease of redbay (Persea borbonia) caused by Raffaelea lauricola. This fungus, harbored in the mycangium of the redbay ambrosia beetle Xyleborus glabratus, is in the form of a budding yeast in the mycangium and a filamentous fungus in galleries of the beetle. Several species also resident in the beetle were described as new to science in 2010: R. ellipticospora, R. fusca, R. subalba, and R. subfusca.

Raffaelea ellipticospora

Raffaelea ellipticospora is a mycangial fungus, first isolated from female adults of the redbay ambrosia beetle, Xyleborus glabratus.

Raffaelea fusca

Raffaelea fusca is a mycangial fungus, first isolated from female adults of the redbay ambrosia beetle, Xyleborus glabratus.

Raffaelea subalba

Raffaelea subalba is a mycangial fungus, first isolated from female adults of the redbay ambrosia beetle, Xyleborus glabratus.

Raffaelea subfusca

Raffaelea subfusca is a mycangial fungus, first isolated from female adults of the redbay ambrosia beetle, Xyleborus glabratus.

Trypodendron

Trypodendron is a genus of ambrosia beetles of the family Curculionidae. There are at least 30 described species in Trypodendron.Some species have reached pest status because they attack freshly sawn timber and degrade the wood.

Trypodendron lineatum

Trypodendron lineatum, known generally as striped ambrosia beetle, is a species of typical bark beetle in the family Curculionidae. Other common names include the two-striped timber beetle, conifer ambrosia beetle, and spruce timber beetle.

Xyleborinus saxeseni

Xyleborinus saxeseni, known generally as the fruit-tree pinhole borer or keyhole ambrosia beetle, is a species of typical bark beetle in the family Curculionidae. Other common names are common Eurasian Ambrosia Beetle, Asian Ambrosia Beetle; Lesser Shot Hole Borer. It is found in North America. X. Saxeseni is primarily a temperature zone species, although it does appears in some areas in more tropical climates. Length is about 2–2.4 mm (0.079–0.094 in), 2.6-3.0 times longer than wide.

It usually attacks unhealthy trees. It hosts in the ornamental trees, stone fruits and timber. Almost all conifers and hardwoods are susceptible. Economic damage to fruit trees has bas been particularly devastating.

Xyleborus (beetle)

With over 500 species, Xyleborus is by far the largest ambrosia beetle genus in the tribe Xyleborini.Xyloborus nowadays includes a number of formerly independent genera. In addition, the genera Coptoborus, Cryptoxyleborus and Euwallacea are often included here, too; this may be correct, as they seem to be closely related. Less often, Ambrosiodmus, Premnobius and Xyleborinus are included in Xyleborus, but they seem to be well distinct; Premnobius might even not belong to the Xyleborini at all.

The different species can be best differentiated by the gallery burrows they build and the tree species they infest. A significant member, X. dispar, causes pear blight.

Xyleborus glabratus

Xyleborus glabratus (redbay ambrosia beetle) is a type of ambrosia beetle invasive to the United States. It has been documented as carrying the fungus that causes laurel wilt, a disease that can kill several tree species in the Lauraceae family, including redbay and avocado.The beetle, first detected in the United States in 2002, is native to Asia and may have arrived in wood products, packing materials or pallets. Laurel wilt has been found in South Carolina and Georgia, and notably in Florida, where it has reached as far south as Dade County and as far west as Bay County. In 2009, state officials in Mississippi confirmed the positive identification of the disease in Jackson County. In 2011, it was confirmed as present in North Carolina and Alabama.

Xylosandrus compactus

Xylosandrus compactus is a species of ambrosia beetle. Common names for this beetle include black twig borer, black coffee borer, black coffee twig borer and tea stem borer. The adult beetle is dark brown or black and inconspicuous; it bores into a twig of a host plant and lays its eggs, and the larvae create further tunnels through the plant tissues. These beetles are agricultural pests that damage the shoots of such crops as coffee, tea, cocoa and avocado.

Xylosandrus crassiusculus

Xylosandrus crassiusculus, known generally as the Asian ambrosia beetle or granulate ambrosia beetle, is a species of tropical bark beetle in the family Curculionidae. It is native to Asia, but is an invasive species in Africa, the Americas, Europe and Oceania.

Xylosandrus germanus

Xylosandrus germanus, known generally as the alnus ambrosia beetle or black stem borer, is a species of ambrosia beetle in the family Curculionidae. The black stem borer is native to eastern Asia, but is an invasive species in Europe and North America. It carries an associated ambrosia fungus, Ambrosiella grosmanniae.

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