Bark beetle

A bark beetle is the common name for the subfamily of beetles Scolytinae.^[1] Previously, this was considered a distinct family (Scolytidae), but is now understood to be a specialized clade of the "true weevil" family (Curculionidae). Although the term "bark beetle" refers to the fact that many species feed in the inner bark (phloem) layer of trees, the subfamily also has many species with other lifestyles, including some that bore into wood, feed in fruit and seeds, or tunnel into herbaceous plants.^[1] Well-known species are members of the type genus Scolytus, namely the European elm bark beetle S. multistriatus and the large elm bark beetle S. scolytus, which like the American elm bark beetle Hylurgopinus rufipes, transmit Dutch elm disease fungi (Ophiostoma). The mountain pine beetle Dendroctonus ponderosae, southern pine beetle Dendroctonus frontalis, and their near relatives are major pests of conifer forests in North America. A similarly aggressive species in Europe is the spruce ips Ips typographus. A tiny bark beetle, the coffee berry borer, Hypothenemus hampei is a major pest on coffee plantations around the world.

Bark beetles Temporal range: Barremian–Recent PreꞒ Ꞓ O S D C P T J K Pg N
Mountain pine beetle, Dendroctonus ponderosae
Scientific classification
Kingdom:	Animalia
Phylum:	Arthropoda
Class:	Insecta
Order:	Coleoptera
Family:	Curculionidae
Subfamily:	Scolytinae Latreille, 1804
Tribes
Cortylini Cryphalini Crypturgini Dryocoetini Hylastini Hylesinini Hypoborini Ipini Phloeosinini Phloeotribini Polygraphini Scolytini Scolytoplatypodini Taphrorychini Thamnurgini Tomicini Xyleborini Xyloterini

Life cycle and morphology

Bark beetles go through four stages of life: egg, larvae, pupae, and adult, with the time to develop often relying on the species as well as the current temperature. While there is variation among species, generally adults first bore into a tree and lay their eggs in the phloem of the tree. This usually occurs in mid to late summer. Once the eggs hatch, the larvae then live in the tree, feeding on the living tissues below the bark, often leading to death of the tree if enough larvae are present. At the end of the larval stage, chambers are usually constructed for the pupae to overwinter until they are ready to emerge as an adult.^[2]

Bark beetles are distinct in their morphology due to their small size and cylindrical shape. Bark beetles also have small appendages, with antennae that can be folded into the body and large mandibles to aid in the excavation of woody tissue. The legs of most bark beetles are very short and can be retracted or folded into the body. The combination of their shape and appendages greatly helps in the excavation of woody tissue. The eyes are also flattened and hypothesized to help see in low-light conditions.^[1]

Description and ecology

 

Mountain pine beetles killed these lodgepole pine trees in Prince George, British Columbia.

Bark beetles feed and breed between the bark and the wood of various tree species. While some species, such as the mountain pine beetle (Dendroctonus ponderosae), do attack living trees, many bark beetle species feed on weakened, dying, or dead spruce, fir, and hemlock.^[3][4] Most restrict their breeding area to one part of the tree: twig, branch, stem, or root collar. Some breed in trees of only one species, while others in numerous species of tree. In undisturbed forests, bark beetles serve the purpose of hastening the recycling and decomposition of dead and dying wood and renewing the forest. However, a few species are aggressive and can develop large populations that invade and kill healthy trees and are therefore known as pests.^[5]

Bark beetles often attack trees that are already weakened by disease, overcrowding, conspecific beetles, or physical damage. In defense, healthier trees may produce sap, resin or latex, which often contains a number of insecticidal and fungicidal compounds that can kill, injure, or immobilize attacking insects. Sap is one of the first lines of defense of pines against bark beetles. Released sap or resins can plug bored holes of bark beetles and seal wounds. Resins also trap insect pests making some initial entry by bark beetles unsuccessful. Chemical compounds can also be induced by tree species that bind with amino acids in the gut of bark beetles, reducing their ability to process woody materials.^[3] When in large quantities, the sheer number of beetles can overwhelm the tree's defenses with resulting impacts on the lumber industry, water quality, fish and wildlife, and property values.^[6]

The oldest known member of the group is Cylindrobrotus from the Early Cretaceous (Barremian) aged Lebanese amber.^[7] A species of the extant mostly Neotropical genus Microborus is also known from the Cenomanian aged Burmese amber of Myanmar.^[8]

Prey relationships

Bark beetles are preyed upon by birds such as woodpeckers,^[9] other beetles such as the black-bellied clerid (Enoclerus lecontei)^[10] and certain other members of family Cleridae,^[11]: 8 flies such as the long-legged flies (Dolichopodidae),^[12] and certain phoretic mites.^[12][13] Phoretic mites use the bark beetle to move from one location to the next,^[12][13] but some of these mite species also prey on the eggs or larvae of the bark beetles or act as parasites.^[13]

Parasitoids

The braconid wasp Spathius canadensis is known to parasitize the native elm bark beetle Hylurgopinus rufipes.^{[11]: 33–35 [14]}

Ambrosia beetles

Some bark beetles form a symbiotic relationship with certain Ophiostomatales fungi, and are named "ambrosia beetles". The ambrosia beetles (such as Xyleborus) feed on fungal "gardens" cultivated on woody tissue within the tree. Ambrosia beetles carry the fungal spores in either their gut or special structures, called mycangia, and infect the trees as they attack them. Once a beetle chooses a tree, they release spores of this fungus along tunnels within the tree. These spores grow and eventually produce fruiting structures to be consumed by the beetles. This can allow for ambrosia beetles to indirectly feed from more tree species due to the reliance on the fungi for food and the fungi's ability to overcome some of the plant's chemical defenses.^[15] While the majority of ambrosia beetles infect dead trees, several species will infect trees considered healthy or under stress.^[1]

Biochemistry

The bark beetle's pheromones, including kairomones, can attract other insects.^[16] The pheromones distinguished as kairomones are hormones, pheromones, or allomones of bark beetles, which in turn are used as a locator by insects that are attracted by it, such as flies, which may intend to harm the bark beetle itself.^[16] These chemicals interact with pine trees^[17] as the bark beetle's host, based on the behavioral, physiological, and biochemical effects of monoterpenes.^[17]

Monoterpenes are a chemical fragrance that plays a significant role in tree-insect interactions, specifically within pine trees. It is an aggregation pheromone that attracts insects to the plant/ tree host, including the bark beetle. Monoterpenes has also been known to prevent fungal growth^[18] and are also toxic to bark beetles at high vapor concentrations.^[17] This latter process demonstrates a defense of pines using monoterpenes against the bark beetle.

Taxonomy

There are around 6,000 described species of bark beetles in 246 genera, placed into 26 distinct tribes.^[19]

As pests

Bark beetles are most commonly recognized by their impact on the lumber industry. Massive outbreaks of mountain pine beetles in western North America after about 2005 have killed millions of acres of forest from New Mexico to British Columbia.^[20] Bark beetles enter trees by boring holes in the bark of the tree, sometimes using the lenticels, or the pores plants use for gas exchange, to pass through the bark of the tree.^[3] As the larvae consume the inner tissues of the tree, they often consume enough of the phloem to girdle the tree, cutting off the spread of water and nutrients. Ambrosia beetles are also known to aid in the spread of pathogens, such as diseases that can cause cankers, further damaging the trees they infect.^[21] Like many other insects, Scolytinae emit pheromones to attract conspecifics, which are thus drawn to trees already colonized by bark beetles. This can result in heavy infestations and eventually death of the tree.^[3][22] Many are also attracted to ethanol produced as a byproduct of microbial growth in the dead woody tissues.^[23] Increases in international trade as well as the use of wood containers for storage has aided numerous species of bark beetle in spreading across the world.^[24] They are also extremely adaptable and able to quickly spread through new environments, as seen in France with eleven different species.^[25] Bark beetle infestations are also predicted to increase with global warming, meaning infestations will most likely increase in frequency as temperatures rise.^[26][27] In the past, fire has been suggested as potential mechanism for controlling bark beetle populations; however, most studies of wildfire after beetle outbreaks have found no effect of beetle-caused tree mortality on wildfire size or severity.^[28][29][30]

Bark beetles can also be transporters of different plant pathogens such as cankers. The transport of the pathogens also result in the increase of fungi, mites and nematodes within the tree.^[31]

Gallery

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  Bark beetle gallery engraving the sapwood

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  Bark beetle galleries with bark showing exit holes

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  Some species produce single winding tracks

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  Bark beetle galleries on a dead American elm

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  Bark beetle trap

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  Manually decorticated trunk of a spruce as protection to bark beetles

See also

• Forest pathology
• Ambrosia beetle
• Xyleborus glabratus
• Euwallacea fornicatus
• Laurel wilt disease

References

1. Kirkendall, Lawrence; Biedermann, Peter H.W.; Jordal, Bjarte (2015). "Chapter 3: Bark Beetles: Biology and Ecology of Native and Invasive Species". Bark Beetles: Biology and Ecology of Native and Invasive Species. Academic Press.
2. Barkley, Yvonne. "Everything you have always wanted to know about bark beetles, but were afraid to ask" (PDF). (PDF) from the original on 2020-08-21.
3. Franceschi, Vincent R.; Krokene, Paal; Christiansen, Erik; Krekling, Trygve (2005-05-03). "Anatomical and chemical defenses of conifer bark against bark beetles and other pests". New Phytologist. 167 (2): 353–376. doi:10.1111/j.1469-8137.2005.01436.x. ISSN 0028-646X. PMID 15998390.
4. Rose, A.H.; Lindquist, O.H. 1985. Insects of eastern spruces, fir and, hemlock, revised edition. Gov’t Can., Can. For. Serv., Ottawa, For. Tech. Rep. 23. 159 p. (cited in Coates et al. 1994, cited orig ed 1977)
5. Blomquist, Gary J.; Figueroa-Teran, Rubi; Aw, Mory; Song, Minmin; Gorzalski, Andrew; Abbott, Nicole L.; Chang, Eric; Tittiger, Claus (2010-10-01). "Pheromone production in bark beetles". Insect Biochemistry and Molecular Biology. 40 (10): 699–712. doi:10.1016/j.ibmb.2010.07.013. ISSN 0965-1748. PMID 20727970.
6. Fettig, Christopher; Klepzig, Kier; Billings, Ronald; Munson, A. Steven; Nebeker, T. Evan; Negrόn, Jose; Nowak, John (Jan 2007). "The effectiveness of vegetation management practices for prevention and control of bark beetle infestations in coniferous forest of the western and southern United States". Forest Ecology and Management. 238 (1): 24–53. doi:10.1016/j.foreco.2006.10.011 – via Science Direct.
7. Kirejtshuk, Alexander G.; Azar, Dany; Beaver, Roger A.; Mandelshtam, Mikhail Yu.; Nel, André (January 2009). "The most ancient bark beetle known: a new tribe, genus and species from Lebanese amber (Coleoptera, Curculionidae, Scolytinae)". Systematic Entomology. 34 (1): 101–112. doi:10.1111/j.1365-3113.2008.00442.x. S2CID 73530299.
8. Cognato, Anthony I.; Grimaldi, David (January 2009). "100 million years of morphological conservation in bark beetles (Coleoptera: Curculionidae: Scolytinae)". Systematic Entomology. 34 (1): 93–100. doi:10.1111/j.1365-3113.2008.00441.x. S2CID 85272919.
9. Latif, Quresh. "Beetles and Birds". Connecting People, Birds and Land for a Healthy World. Retrieved 2022-10-31.
10. "Bark Beetles Management Guidelines--UC IPM". ipm.ucanr.edu. Retrieved 2022-10-31.
11. Kaston, B.J. (February 1939). The Native Elm Bark Beetle Hylurgopinus rufipes (Eichhoff) in Connecticut (PDF) (Report). New Haven: Connecticut Agricultural Experiment Center. Bulletin 420. Retrieved 9 January 2023 – via ct.gov.
12. Wegensteiner, Rudolf; Wermelinger, Beat; Herrmann, Matthias (2015). "Chapter 7 - Natural Enemies of Bark Beetles: Predators, Parasitoids, Pathogens, and Nematodes". In Vega, Fernando E.; Hofstetter, Richard W. (eds.). Bark Beetles: Biology and Ecology of Native and Invasive Species. San Diego: Academic Press. pp. 247–304. doi:10.1016/b978-0-12-417156-5.00007-1. ISBN 978-0-12-417156-5.
13. Cilbircioğlu, Cihan; Kovač, Marta; Pernek, Milan (May 2021). "Associations of Phoretic Mites on Bark Beetles of the Genus Ips in the Black Sea Mountains of Turkey". Forests. 12 (5): 516. doi:10.3390/f12050516. ISSN 1999-4907.
14. Kaston, J. (1936). "Notes on Hymenopterous Parasites of Elm Insects in Connecticut" (PDF). In Britton, W.E. (ed.). Connecticut State Entomologist Thirty-Sixth Report (Report). New Haven: Connecticut Agricultural Experiment Station. pp. 351–361. Bulletin 396. Retrieved 9 January 2023 – via ct.gov.
15. Kirkendall, Lawrence R.; Biedermann, Peter H.W.; Jordal, Bjarte H. (2015), "Evolution and Diversity of Bark and Ambrosia Beetles", Bark Beetles, Elsevier, pp. 85–156, doi:10.1016/b978-0-12-417156-5.00003-4, ISBN 978-0-12-417156-5, retrieved 2021-03-30
16. Klowden, Marc J. (2013-01-01), Klowden, Marc J. (ed.), "Chapter 12 - Communication Systems", Physiological Systems in Insects (Third Edition), San Diego: Academic Press, pp. 603–647, doi:10.1016/b978-0-12-415819-1.00012-x, ISBN 978-0-12-415819-1, retrieved 2022-10-31
17. Seybold, Steven J.; Huber, Dezene P. W.; Lee, Jana C.; Graves, Andrew D.; Bohlmann, Jörg (2006-02-01). "Pine monoterpenes and pine bark beetles: a marriage of convenience for defense and chemical communication". Phytochemistry Reviews. 5 (1): 143–178. doi:10.1007/s11101-006-9002-8. ISSN 1572-980X. S2CID 34160711.
18. Fang, Jiaxing; Liu, Man; Zhang, Sufang; Liu, Fu; Zhang, Zhen; Zhang, Qinghe; Kong, Xiangbo (2020-10-07). Foyer, Christine (ed.). "Chemical signal interactions of the bark beetle with fungal symbionts, and host/non-host trees". Journal of Experimental Botany. 71 (19): 6084–6091. doi:10.1093/jxb/eraa296. ISSN 0022-0957. PMID 32589724.
19. Pistone, Dario; Gohli, Jostein; Jordal, Bjarte H. (April 2018). "Molecular phylogeny of bark and ambrosia beetles (Curculionidae: Scolytinae) based on 18 molecular markers: Molecular phylogeny of bark and ambrosia beetles". Systematic Entomology. 43 (2): 387–406. doi:10.1111/syen.12281. hdl:1956/17546. S2CID 90571090.
20. Jim Robins (17 Nov 2008). "Bark Beetles Kill Millions of Acres of Trees in West". The New York Times.
21. Li, You; Skelton, James; Adams, Sawyer; Hattori, Yukako; Smith, Matthew E.; Hulcr, Jiri (2020). "The Ambrosia Beetle Sueus niisimai (Scolytinae: Hyorrhynchini) is Associated with the Canker Disease Fungus Diatrypella japonica (Xylariales)". Plant Disease. 104 (12): 3143–3150. doi:10.1094/pdis-03-20-0482-re. ISSN 0191-2917. PMID 33136520. S2CID 225788674.
22. "Bark Beetle FAQs". Ready for Wildfire. Retrieved 2022-10-31.
23. Lindelöw, Åke; Risberg, Birger; Sjödin, Kristina (1992). "Attraction during flight of scolytids and other bark- and wood-dwelling beetles to volatiles from fresh and stored spruce wood". Canadian Journal of Forest Research. 22 (2): 224–228. doi:10.1139/x92-029. ISSN 0045-5067.
24. Brockerhoff, E. G.; Liebhold, A. M. (2017-07-20). "Ecology of forest insect invasions". Biological Invasions. 19 (11): 3141–3159. doi:10.1007/s10530-017-1514-1. ISSN 1387-3547. S2CID 34192154.
25. Barnouin, Thomas; Soldati, Fabien; Roques, Alain; Faccoli, Massimo; Kirkendall, Lawrence; Moutter, Raphaëlle; Daubree, Jean-Baptiste; Noblecourt, Thierry (2020-11-09). "Bark beetles and pinhole borers recently or newly introduced to France (Coleoptera: Curculionidae, Scolytinae and Platypodinae)". Zootaxa. 4877 (1): 51–74. doi:10.11646/zootaxa.4877.1.2. ISSN 1175-5334. PMID 33311325. S2CID 228840630.
26. Andreas Sommerfeld; Werner Rammer; Marco Heurich; Torben Hilmers; Jörg Müller; Rupert Seidl (2020-07-20). "Author response for "Do bark beetle outbreaks amplify or dampen future bark beetle disturbances in Central Europe?"". doi:10.1111/1365-2745.13502/v3/response1. S2CID 242935910. {{cite journal}}: Cite journal requires |journal= (help)
27. "Bark Beetles and Climate Change in the United States | Climate Change Resource Center". www.fs.usda.gov. Retrieved 2022-10-31.
28. Harvey, Brian J.; Donato, Daniel C.; Romme, William H.; Turner, Monica G. (2013-11-01). "Influence of recent bark beetle outbreak on fire severity and postfire tree regeneration in montane Douglas-fir forests". Ecology. 94 (11): 2475–2486. doi:10.1890/13-0188.1. ISSN 1939-9170. PMID 24400499. S2CID 7023088.
29. Meigs, Garrett W.; Campbell, John L.; Zald, Harold S. J.; Bailey, John D.; Shaw, David C.; Kennedy, Robert E. (2015-07-01). "Does wildfire likelihood increase following insect outbreaks in conifer forests?" (PDF). Ecosphere. 6 (7): art118. doi:10.1890/ES15-00037.1. ISSN 2150-8925.
30. Harvey, Brian J.; Donato, Daniel C.; Turner, Monica G. (2014-10-21). "Recent mountain pine beetle outbreaks, wildfire severity, and postfire tree regeneration in the US Northern Rockies". Proceedings of the National Academy of Sciences. 111 (42): 15120–15125. Bibcode:2014PNAS..11115120H. doi:10.1073/pnas.1411346111. ISSN 0027-8424. PMC 4210318. PMID 25267633.
31. "Bark Beetles and Associated Issues | | Wisconsin DNR". dnr.wisconsin.gov. Retrieved 2022-11-29.

External links and further reading

 

Wikimedia Commons has media related to Scolytinae.

 

Wikispecies has information related to Scolytinae.

• American and Mexican Bark and Ambrosia beetles
• Nordhaus, Hannah. Bark Beetle Outbreaks in Western North America: Causes and Consequences. University of Utah Press: Salt Lake City, 2009. ISBN 978-0-87480-965-7