Plant Condition

Plants in a wide range of physiological conditions may be subject to colonization by borers. Although some species of borers use healthy hosts or healthy host tissues, plants that are suffering from some type of stressful condition either attract or inhibit further dispersal behavior by many other borer species. Insects that bore into tender tips and stems frequently colonize young and vigorously growing plants. Consequently, younger plants may suffer more damage than mature plants. Open wounds or stressed, damaged, or weakened plant tissues may be subject to invasion. Weakened or stressed host plants may result from chronic growing conditions (poor-quality site) or from acute detrimental changes (e.g., fire, flood, drought, lightning strikes). Infections by pathogens, particularly plant pathogenic fungi, nematodes, and parasitic plants, weaken host plants and increase their susceptibility to subsequent borer infestations. In addition, previous infestation by other insect herbivores may weaken the host plant and increase susceptibility to subsequent borer colonization. Recently killed and dying trees are particularly suitable for colonization by a range of borers. For example, there are several species of wood wasps and flatheaded wood borers that are attracted to trees that have been recently killed by fires. A wide range of borers have developed complex relationships with tree-killing pathogens and are responsible for transmitting the pathogens into the host trees. Scolytid bark beetles transmit species of pathogenic Ophiostoma and Ceratocystis fungi into a variety of hosts (e.g., Scolytus scolytus, S. multistriatus, and Hylurgopinus rufipes transmit Ophiostoma ulmi, the causal agent of Dutch elm disease). Cerambycids in the genus Monochamus are responsible for transmitting the nematode, Bursaphelenchus xylophilus, the pathogen causing pine wilt disease, into susceptible host pines. Females of the European woodwasp, Sirex noctilio, inject a phytotoxin and spores of the pathogenic fungus Amylostereum areolatum into susceptible host trees during oviposition. Borers that are adapted to colonize the woody tissues of dead or dying plants may also colonize trees that have been cut during commercial logging or even timber that has been milled into lumber. It is not unusual for adult borers to emerge from products or materials constructed from infested wood that has not been kiln dried or otherwise treated to kill the infesting insects.

See Also the Following Articles

Forest Habitats • Integrated Pest Management • Plant Diseases and Insects

Further Reading

Creffield, J. W. (1996). "Wood Destroying Insects: Wood Borers and Termites," 2nd ed. CSIRO Australia, Collingwood.

Furniss, R. L., and Carolin, V. M. (1980). "Western Forest Insects." U.S. Department of Agriculture Forest Service, Washington, DC. [Miscellaneous Publication 1339]. Hanks, L. M. (1999). Influence of the larval host plant on reproductive strategies of cerambycid beetles. Annu. Rev. EntomoL 44, 483—505. Johnson, W. T., and Lyon, H. H. (1988). "Insects That Feed on Trees and

Shrubs." Cornell University Press, Ithaca, NY. Paine, T. D., Raffa, K. F., and Harrington, T. C. (1997). Interactions among scolytid bark beetles, their associated fungi and live host conifers. Annu. Rev. EntomoL 42, 179-206. Solomon, J. D. (1995). "Guide to the Insect Borers of North American Broadleaf Trees and Shrubs." U.S. Department of Agriculture Forest Service, Washington, DC. [Agricultural Handbook 706] U.S. Department of Agriculture Forest Service. (1985). "Insects of Eastern Forests." U.S. Department of Agriculture Forest Service, Washington, DC. [Miscellaneous Publication 1426]

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