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Goldspotted Oak Borer

 

Agrilus auroguttatus Schaeffer -- Coleoptera:  Buprestidae

 

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       The Goldspotted Oak Borer is a beetle that is native to oak forests of Southeastern Arizona, and a closely related species (Agrilus coxalis), occurs in Central Mexico, and Northern Guatemala (Coleman & Seybold 2008).  Since 2002, the goldspotted borer has contributed to the mortality of more than 80,000 trees over approximately 4,900 square-kilometers, and this infested area continues to increase as the borer population spreads.  In its native range, the borer is not a pest that may be due to efficient population control by natural enemies and natural levels of resistance by oak species that have existed for many centuries with the insect.

 

       The borer was first detected in San Diego County, California in 2004 by the California Department of Food and Agriculture during a survey for exotic woodborers.  Then in 2008 it was found attacking three species of oak in the Cleveland National Forest in San Diego County: coast live oak (Quercus agrifolia), canyon live oak (Q. chrysolepis), and California black oak (Q. kelloggii).

 

       Although the U. S. Dept. of Agriculture Forest Service in the Cleveland National Forest had aerially mapped elevated levels of oak mortality since 2002, it was not known that the borer could be the cause of such mortality until 2008 when it was confirmed as the cause of oak death, although drought was probably a contributing factor.

 

       Museum records from southeastern Arizona, southern Mexico, and northern Guatemala indicated that the borer has been collected from these areas since the late 1800's and these regions collectively form its native range. 

 

       The borer's eggs are about 1 mm in width, oval shaped and with a flat bottom.  They are white initially, but turn a brownish color within 2-3 days, and hatch within 10-14 days. In the laboratory, eggs have been observed to be laid individually on both artificial surfaces and in oak bark crevices.  The small size of eggs have precluded observation in the field, but they are most likely deposited in bark crevices like other Agrilus species.  Once eggs hatch, larvae burrow into the tree where they feed under the bark, primarily in the cambium layer.

 

       Mature larvae do not have legs and are about 18 mm long and 3 mm wide.  There is a round head with hardened mandibles,  and they possess two pincher-like spines at the tip of the abdomen, which separates them from other beetle larvae feeding on oaks.  The adults feed on oak foliage.

 

       Studies in southern California found one generation each year with mature larvae present in trees beginning in late May. Larvae and pupae have been observed beneath bark as late as October, suggesting that some small fraction of the population may require more than one year to develop.

 

REFERENCES:

 

Coleman, T. W. & S. J. Seybold.  2011.  Collection history and comparison of the interactions of the goldspotted oak borer, Agrilus auroguttatus Schaeffer (Coleoptera: Buprestidae), with host oaks in southern California and southeastern Arizona.  The Coleopterists Bulletin 2011.

 

Coleman, T. W. & S. J. Seybold.  2008.  New pest in California: The goldspotted oak borer, Agrilus coxalis Waterhouse.   USDA Forest Service, Pest Alert, R5-RP-022, October 28, 2008, 4 pp.

 

Coleman, T. W., N. E. Grulke, M. Daly, C. Godinez, S. Schilling, P. Riggan, S. J. Seybold.  2011.  Coast live oak, Quercus agrifolia, susceptibility and response to goldspotted oak borer, Agrilus auroguttatus, injury in southern California.  Forest Ecology and Management.

 

Furniss, R. L. & V. M. Carolin.  1977.  Western Forest Insects.  United States Department of Agriculture, Forest Service. Miscellaneous Publication No. 1339:  654 pp.

 

Gibson, G. A. P.  2010.  Calosota Curtis (Hymenoptera, Chalcidoidea, Eupelmidae) – review of the New World and European fauna including revision of species from the West Indies and Central and North America.  Zoo Keys 55:  1-75.

 

Haack, R. A., T. R. Petrice  & A. C. Wiedenhoeft.  2010.  Incidence of bark and wood-boring insects in firewood: A survey at Michigan’s Mackinac Bridge.  Journal of Economic Entomology 103:  1682–1692.

 

Hespenheide, H. A.  1979.  Nomenclature notes on the Agrilinae (Buprestidae). IV.  The Coleopterists Bulletin 33:  105-120.

 

Hespenheide, H. A. & C. L. Bellamy.  2009.  New species, taxonomic notes, and records for Agrilus Curtis (Coleoptera: Buprestidae) of México and the United States.  Zootaxa 2084:  50–68.

 

Hishinuma, S., T. W. Coleman, M.L. Flint  & S. J. Seybold.  2011.  Goldspotted oak borer: Field identification guide,   University of California Agriculture and Natural Resources, Statewide Integrated Pest Management Program, 6 pp., January 13, 2011.

 

Krischik, V.  &  J. Davidson.  2007.  IPM (Integrated Pest Management) of Midwest. Landscapes. Pests of Trees and Shrubs.  University of Minnesota, Online Extension Publication, January 31, 2007.

 

Liu, H., L. S. Bauer, D. L. Miller, T. Zhao, R. Gao, L. Song, Q. Luan, R. Jin & C. Gao.  2007.  Seasonal abundance of Agrilus planipennis (Coleoptera: Buprestidae) and its natural enemies Oobius agrili (Hymenoptera: Encyrtidae) and Tetrastichus planipennis (Hymenoptera: Eulophidae) in China.  Biological Control 42:  61-71.

 

Quicke, D. L. J. & M. J. Sharkey.  1989.  A key to and notes on the genera of Braconinae (Hymenoptera: Braconidae) from America north of Mexico with descriptions of two new genera and three new species.  The Canadian Entomologist 121:  33–36.

 

Solomon. J. D.  1995.  Guide to Insect Borers of North American Broadleaf Trees and Shrubs.  USDA Forest Service, Agricultural Handbook No.706, Washington, D.C., 735 pp.

 

Schaeffer, C.  1905.  Some additional new genera and species of Coleoptera found within the limit of the United States.   Museum of the Brooklyn Institute of Arts and Sciences, Science Bulletin 1 (7):  141–179.

 

USDA Forest Service.  2010.   Biological Control of the Emerald Ash Borer.  Northern Research Station (NRS),

 

Vansteenkiste, D. V., L. Tirry, J. Van Acker & M. Stevens.  2005.  Predispositions and symptoms of Agrilus borer attack in declining oaks.  Annals of Forest Science 61:  815–823.

 

Waterhouse, C. O.  1889.  Insecta. Coleoptera. Serricornia. 62. Agrilus coxalis.  Biologia Centrali-Americana, Vol. 3 (1):  1, April 1889, p. 89.

 

Westcott, R. L.  2005.  A new species of Chrysobothris Eschscholtz from Oregon and Washington, with notes on other Buprestidae (Coleoptera) occurring the United States and Canada.   Zootaxa 1044:  1–15.