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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. |