Goldspotted Oak Borer Survey Program

The invasive goldspotted oak borer (GSOB) beetle was first detected in the San Bernardino Mountains in the community of Oak Glen in 2018. Following this detection,  IERCD began offering free GSOB services to residents to help slow the spread of GSOB and minimize its impacts. These services include surveying oak trees for GSOB, providing management recommendations, and distributing educational resources. During a survey, IERCD staff inspect individual trees on a resident’s property and collect information on tree health and potential hazards. Following the survey, staff provide the resident with a map of the inspected trees and management recommendations if GSOB was found. Since 2018, IERCD has surveyed over 10,000 individual oak trees! The survey program has been supported primarily through funding from the Regional Forest and Fire Capacity (RFFC) Program, with additional funding contributions from U. S. Forest Service’s State, Private, and Tribal Forestry, National Forest Foundation, CAL FIRE, and the Natural Resources Conservation Service.

If you reside within IERCD’s boundary (see map below), contact IERCD's Forest Ecologist, Jocelyn Perez via email or phone (jperez@iercd.org, 909-654-5744) to schedule your free GSOB survey. Unsure if you reside within IERCD's boundary? Check out our interactive mapping tool by clicking here. 

Management Support

Depending on the level of GSOB infestation, IERCD may recommend management activities such as removal of highly infested trees or preventative treatments to protect oak trees on a property.  As funding allows, IERCD works with residents to facilitate the removal of oak trees with high infestations using best management practices. Where possible, IERCD also connects residents with other resources through our partners including CAL FIRE crews and the Mountain Rim Fire Safe Council's Hazardous Dead Tree Removal Program. To receive management support, residents must first receive a GSOB survey by IERCD staff (see above to schedule a free survey). 

Management activities by IERCD have been supported by the CAL FIRE  Southern California Regional Pilot Block Grant and the U.S. Forest Service Invasive Species Program.

Learn More About Goldspotted Oak Borer

The goldspotted oak borer (GSOB), Agrilus auroguttatus, is a flathead beetle that is native to southeastern Arizona but was likely introduced to California via infested firewood. Now, native oak woodlands throughout the state are at risk due to the rapid rate of spread and aggressive feeding behavior of this pest. 

Mated females lay 0.01 inches wide eggs on mature oak trees, and upon hatching, the larvae burrow below the bark. The larvae feed on the cambium layer, creating meandering galleries that disrupt the tree's nutrient transport system. Mature larvae will tunnel near the bark surface until they pupate in October. Adults emerge from mid-May to September, chewing through the bark, forming a distinctive 0.15-inch-wide D-shaped exit hole. The emergence holes are the primary method of identification. Other visible external symptoms of GSOB infestation include thinning of the tree canopy, which progressively worsens over time, as well as wet brown, black, or red stains on the bark. 

The beetle completes one generation each year, and while some trees are capable of withstanding several years of attack, the aggressive feeding by successive generations of GSOB eventually kills the tree if left untreated.

What Can You Do?

• Volunteer at a local GSOB Blitz: Participate in a community powered effort to detect GSOB, while making a real impact. 
• Don’t Move Fire Wood: GSOB or other invasive species can be hiding in firewood. Buy heat-treated firewood or get firewood local to where you plan to burn it. 
• Report potential infestation: Fill out the linked UCANR form, contact IERCD or post a picture on iNatualist if you suspect an oak is infested with GSOB. 
• Help Us Spread the Word!: Request educational materials through IERCD and spread awareness to friends, family and neighbors regarding the risks posed by GSOB.

Goldspotted Oak Borer Distrubution Map

The map below shows the known distribution of GSOB within IERCD’s boundary, as well as areas susceptible to infestation (last updated September 2026). The red pins mark communities where GSOB has been detected. The pink, yellow, and green areas show the distribution of the three oak tree species in the area, which can all be infested by GSOB. 

Click here to view all confirmed areas of infestation within California. 

 

Other Resources: click to download