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 signiﬁcant 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 ﬂy 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-ﬁr 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. [...]
[...] While one species of bark beetle has been shown to recognize tree suitability in ﬂight, it appears that beetles of other species must actually land on a tree, and even consume part of it, to determine its suitability. Such a search process may be very time- and energy-consuming, and many species of bark beetles also respond positively to volatiles produced by breeding conspeciﬁcs (pheromones). This is true for species that colonize either dead or living host trees. Bark beetles have several strategies for coping with plant defenses against herbivory and disease. [...]
[...] Bark beetles have a fascinating diversity of breeding systems, including monogamy, polygyny, inbreeding polygyny (often associated with haplo- diploidy), and parthenogenesis. Monogamy and polygyny are clearest when males initiate breeding sites, with a species-typical number of females sharing the same nuptial chamber. Males contribute by removing debris produced by tunneling females and guarding the entrance against predators. Males may remain for some or all of the oviposition and larval development periods. When females initiate the breeding site, there is generally only a single female per nuptial chamber (monogyny), but males generally depart early in oviposition and may mate again elsewhere. [...]
[...] Host Plants Evolutionarily, bark beetles appear to have originated in conifers, and many of the most conspicuous and economically important species breed in conifers. However, most bark beetle species (approximately breed in angiosperms. As their name suggests, many bark beetles breed within the inner bark (phloem) of tree boles or branches. While these species are often the most important economically, phloem-feeding is characteristic of fewer than half of all bark beetle species. More commonly, bark beetles develop within tree xylem where they feed upon symbiotic fungi (xylomycetophagy). [...]
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