Author: Anne Buckelew Cumming, USDA Forest Service
Goldspotted oak borer (GSOB) is believed to have been transported via firewood or other human activity into southern California, specifically San Diego County, from Arizona, where it is considered a native beetle (ArborJet 2009, Smith 2009). First detected in 2004, it has caused extensive damage to coast live oaks, canyon live oaks and California black oaks in and around the Cleveland National Forest. It was determined to be the cause of oak mortality dating back to 2002. More than 20,000 trees on 620,000 acres have been affected. As of 2011, this insect was not a regulated pest under the Animal Plant Health Inspection Service, but was being watched closely (Center for Invasive Species Research 2011).
Goldspotted oak borer is a native insect found in Arizona. Its spread to California and its infestation of coast live oak, canyon live oak and California black oak has proved problematic and has resulted in extensive mortality of those species in San Diego County, California, USA (Smith 2009, Hespenheide et al. 2009).
Three oak species in southern California are at risk from goldspotted oak borer.
Quercus agrifolia Nee (coast live oak) occurs in California and northern Mexico. It is distributed from Mendocino County, California, south to Baja California. Limited inland populations occur along watercourses in the Central Valley. Coast live oak is also found on the Channel Islands of Santa Rosa and Santa Cruz (Steinburg 2002).
Quercus chrysolepis (canyon live oak) is native to Oregon, California, Nevada, Arizona, and Mexico. It is distributed from southwestern Oregon south through California and into northern Baja California, Mexico. It is the most widely distributed oak in California, occurring in the Klamath Mountains, the Coast Ranges, western slopes and eastern slope canyons (scattered) of the Sierra Nevada, and the Transverse and Peninsular ranges(Tollefson 2008).
Quercus kelloggii Newb. (california black oak) is native to Oregon and California. It is the most widely distributed of the western oaks. It grows in the foothills and lower mountains of southern Oregon and California, with a north-south range of about 780 miles (1,260 km). It is contiguously distributed from west-central Oregon, south to just north of the Mexican border in the Agua Tibia Mountains of San Diego County, California (Fryer 2007).
Adult goldspotted oak borers are a dull green color with a dark metallic sheen and have 6 yellow/gold spots on the wings. They have a bullet shape, 3/8th inches (10mm) long and 1/16th inches (2mm) wide. The larvae are slender, white, and have no legs. The tip of abdomen has two spines that look like pinchers. Larvae are about 11/16th inches (18mm) long by 1/8th inches (3 mm) wide. Larvae emerge from the tree through small (1/8th inches (3mm)) D-shaped holes. Pupae look similar to adults in size and shape, but are white (Smith 2009)
Plant Response and Damage
Eggs are laid on or in the bark of the oak trees. Larvae emerge and burrow further into the bark to feed on phloem. The main stem and large branches are the most common sites of activity (Center for Invasive Species Research 2011).
Plant response is dieback and eventually tree death due to restricted movement of nutrients through the vascular tissues of the tree. Trees with GSOB produce copious amounts of sap which oozes from under the bark. Staining occurs and is either black or red (Arborjet 2009). Infestations have been noted only in oaks of large sizes and have not been found in oaks less than 12 cm d.b.h. (Smith et al. 2010).
Timing of sampling
Goldspotted oak borers are detected through trapping of adults. The adult flight period is from June to November in Southern California with larvae maturing from May to October. GSOB are assumed to have one generation per year, although this has not been confirmed (Smith 2009).
Survey methods: Collections made with funnel traps – state survey in 2004. Attractant-baited panel traps. Destructive sampling to recover life stages. Surveys in 2004 by the California Department of Food and Agriculture used funnel traps for a statewide exotic borer surveys where GSOB was found. In addition, panel traps with attractant bait have been successful for adult beetle collections, while destructive sampling of oaks must be used to recover the range of life stages (Smith 2009).
Signs of infestation include the presence of emergence holes and larval galleries. Woodpecker damage, bark staining, premature leaf drop, branch dieback, and crown thinning are examples of GSOB symptoms (Center for Invasive Species Research 2011).
Widespread treatment of woodborers such as GSOB and others is difficult. Outreach and education to the public and to arborist is currently the best method for reducing the spread of the insects. Logs, wood debris and firewood should not be moved or transported since the insects may be present under the bark.
As of 2011, there were no state or federal regulations to control or minimize the spread of GSOB. There are no restrictions on the movement of infested wood or other materials (Center for Invasive Species Research 2011).
Removal of dead oak trees is imperative for safety and to reduce hazards. Disposal of GSOB wood could follow best management practices in place for emerald ash borer infested materials, but mandates for those practices are in place at this time (ArborJet 2009).
- Arborjet. 2009. Arborjet Blog: The Goldspotted Oak Borer. Author. Retrieved March 25, 2010, from http://www.arborjet.com/blog/2009/10/the-goldspotted-oak-borer/
- Center for Invasive Species Research. 2011. The Goldspotted Oak Borer, Agrilus coxalis Waterhouse. University of California - Riverside. Retrieved March 11, 2011, from http://cisr.ucr.edu/goldspotted_oak_borer.html [2011, March 11].
- Fryer, Janet L. 2007. Quercus kelloggii. In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Available: http://www.fs.fed.us/database/feis/ [2011, March 11].
- Hespenheide, H. A., & Bellamy, C. L. 2009. New species, taxonomic notes, and records for Agrilus Curtis (Coleoptera: Buprestidae) of México and the United States. Zootaxa, 2084, 50-68. Available: http://www.mapress.com/zootaxa/2009/1/zt02084p068.pdf. [2010, March 23]
- Smith, S. (Preparer). 2009. Goldspotted Oak Borer Strategic Plan. 1-27. United States Department of Agriculture, Forest Service, Forest Health Protection. Available: http://www.fs.fed.us/r5/spf/fhp/socal/Goldspotted%20Oak%20Borer%20Strategic%20Plan%20September%202009.pdf [2010, March 25].
- Smith, Sheri L., Coleman, Tom W., Scott, Thomas A. 2010. Individual Pest Risk Assessment Goldspotted Oak Borer. R5-FHP-2010-01. Available http://www.fs.fed.us/foresthealth/technology/pdfs/GSOB_pest_Risk_Analysis.pdf [2011, March 11].
- Steinberg, Peter D. 2002. Quercus agrifolia. In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Available: http://www.fs.fed.us/database/feis/ [2011, March 11].
- Tollefson, Jennifer E. 2008. Quercus chrysolepis. In: Fire Effects Information System. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Available: http://www.fs.fed.us/database/feis/ [2011, March 11].