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Bark beetles

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  1. Introduction.
  2. Taxonomy.
  3. Life cycle.
  4. Host plants.
    1. Colonizing post plants.
  5. Factors limiting population growth.
  6. Ecosystem processes.
    1. Fire.
    2. Forest succession.
    3. Decomposition.
  7. Management options.
  8. Conclusion.

Bark beetles are small, dark, cylindrical beetles, usually less than 7mm long. As their name implies, they are usually associated with woody plants. Despite their small size and modest appearance, they have an intriguing assemblage of feeding and breeding habits, some of which result in signi?cant economic losses to forest and agricultural industries. This article reviews the taxonomy, life cycle, host?plant interactions and ecosystem consequences of bark beetles, concluding with management options. Bark beetles have commonly been considered a family, Scolytidae, but recent taxonomy places them as a subfamily, Scolytinae, within the weevil family Curculionidae. Major characteristics that are shared with weevils include elbowed, clubbed antennae, larvae that feed within plant tissues, and the loss of the development of legs in larvae. The Scolytinae and closely related Platypodinae differ from typical weevils in their oviposition behavior: adults bore deeply into plant tissues to oviposit, while typical weevils use their elongated rostrum to create egg niches from the surface of the plant.

[...] As mentioned, the breeding habitat of many bark beetles is no longer suitable after one generation, requiring dispersal every generation. Suitable hosts are typically rare, particularly for those bark beetles species relying on trees lacking defenses but with undeteriorated tissues, such as windfalls. While dispersal mortality cannot be observed directly, estimates from equilibrium population models and changes in sex ratio between emerging and breeding beetles suggest that more than half of beetles die during dispersal. This is despite the ability of many species to ?y 40 km or more. [...]

[...] Decomposition Bark beetles are expected to hasten decomposition because they penetrate the wood material and are vectors for many species of fungi, but few studies have tested this. Douglas-?r beetles, D. pseudotsugae, had a small effect on log decomposition after 10 years, with wood borers contributing much more. Decomposition of spruce in Finland, as measured by percentage mass loss over 30 months, was positively correlated with the number of beetle attacks, although the difference in mass loss between logs with and without exposure to beetles was not large. [...]

[...] Beetles can be deterred from settling on trees, or even in stands, by conspeci?c antiaggregation pheromones, pheromones of competitor bark beetle species, or nonhost volatiles. For species that require high densities of beetles to overcome tree defenses, even some deterrence might allow trees to defend against beetle attacks. Conclusion A preventive approach to bark beetle control is to manage stands and landscapes to prevent the development of large beetle populations. However, by de?nition, pest species use trees that people want, so any plan to make host trees dif?cult for beetles to ?nd will usually compromise the economy of harvest. [...]

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