Goldspotted oak borer: what the agencies record

This page reports what the official source says. It is not legal advice: ask the office named here. It does not identify what is wrong with any tree and does not say what should be done about one. The goldspotted oak borer, Agrilus auroguttatus, is a flatheaded borer whose larvae feed under the bark of oaks in southern California. Each section names its source, all read on October 9, 2026. The parent page, insect pests of trees, compares it with the other pests on the list, and oak galls covers a different group of oak insects.

Names and origin

The University of California Statewide Integrated Pest Management Program, called UC IPM, describes a flatheaded borer introduced to San Diego County in the late 1990s or early 2000s from its native range in southeastern Arizona, probably on oak firewood moved from Arizona or northern Mexico. The California Department of Food and Agriculture, called CDFA, says the insect has been known in California since 2004 and gives the same firewood explanation, adding that large stretches of unsuitable habitat lie between San Diego County and Arizona, and that flight-mill tests gave an average flight of about 790 m in 24 hours. A Purdue University survey datasheet from 2013 records a taxonomy change: the insect was once listed under the Mexican species Agrilus coxalis and was returned to species rank as A. auroguttatus in 2011.

Which oaks it attacks

UC IPM says the borer attacks only oaks and prefers the red oak group, naming coast live oak and California black oak, with canyon live oak also infested and Engelmann oak only very rarely. It says mature trees are preferred, that trees of about 10 inches in breast-height diameter are occasionally attacked, that it is rarely recorded under 5 inches, and that trees of 18 inches or more are the most likely to be killed. CDFA lists coast live oak, California black oak and canyon live oak as the main hosts, adds that laboratory work suggests interior live oak may be a host, and says cork oak, valley oak and blue oak were fed on in the laboratory but are reported infested in the field at much lower densities. In the native range CDFA lists Emory oak and silverleaf oak as hosts and says the rate of infestation in Arizona was reported as 4 percent. Purdue lists the primary hosts as coast live, canyon live, Engelmann and California black oak and says the host range has not been well studied. The blue oak, which CDFA lists among the oaks fed on in the laboratory, has its own page: blue oak.

Stages and life cycle

Stage	What UC IPM records
Adult	About 10 millimeters long and 2 millimeters wide, bullet-shaped, black or iridescent green with six gold spots on the wing covers and two gold spots on the edge of the thorax; rarely seen on trees
Egg	Under 0.25 millimeter, brown, laid singly or in clusters on the bark surface or in bark fissures; extremely hard to find
Larva	White and legless, with two pincher-like spines at the tip of the abdomen; about 2 millimeters at hatching and about 20 millimeters when mature; feeds at the boundary of the xylem and phloem, girdling the cambium
Pupa	Roughly adult size, white and soft at first, in the outer bark from late April through July

UC IPM says the insect is believed to have one generation a year in southern California. Females lay eggs mainly from June through September, the first-stage larvae hatch in about two weeks, and three more larval stages follow. Mature larvae fold into a hairpin shape in pupal cells near the bark surface and can stay in that stage from October to as late as June. Adults emerge from mid-May to September, with the most flight from late June to early July, and must feed on oak foliage for about two weeks before they can breed. CDFA gives about one year for the cycle, with some evidence of longer and shorter ones, and says larval feeding leads to tree death after 3 to 5 years, or sooner if the tree is weakened. Purdue, citing 2008 data, gives a flight season of June to October with a peak in late June.

Signs the sources list

UC IPM lists crown thinning and dieback, dark stains or oozing red sap on the trunk and larger branches, bark removed by woodpeckers that reveals pink-red phloem, and D-shaped emergence holes about 4 millimeters wide, mostly in the lower 10 feet of the trunk and sometimes more than 100 on a heavily infested tree. It calls the D-shaped holes the most definitive indicator and says staining and crown thinning alone do not always mean the borer is present. It names other causes of similar staining, including the sudden oak death pathogen and the western oak bark beetle, and says the borer's frass is tightly packed, granular and usually black. CDFA lists crown thinning, feeding galleries and patches of dead phloem that produce reddish-brown sap, and Purdue gives the exit holes as about 3 millimeters wide.

Where it is recorded

CDFA records the borer in Los Angeles, Orange, Riverside, San Bernardino and San Diego counties, records no interceptions in California, and reports infestation rates above 90 percent in some San Diego County areas, mortality of 45 percent, and over 80,000 trees killed in the state. The University of California site on the borer reports confirmed finds in isolated spots in Riverside, Orange, Los Angeles, San Bernardino and Ventura counties besides the San Diego County core. EPPO, the European plant protection organisation, last updated its distribution record on June 17, 2021 and lists the borer as present in Arizona and California, present in Mexico, and absent in Belgium, Lithuania and Slovenia.

On damage, the sources differ on one point. Purdue notes that drought stress may predispose trees to the borer, while CDFA says a study found no evidence that drought stress predisposed coast live oak and adds that fungal pathogens may be involved in the death of infested oaks. CDFA also says the importance of drought and fungi in the tree deaths is not completely understood.

Regulated status

CDFA's pest rating profile records a rating of B as of September 30, 2022, replacing an earlier Q rating. It says the borer was not the subject of eradication efforts and that eradication does not appear to be practical. Under its rating system the profile gives a final score of Low (8) with a consequences-of-introduction score of Medium (9). EPPO records an A1 list entry for Türkiye (Turkey) from 2016, and a place on its own alert list from 2013 until 2017. The profile records a rating, not a rule on moving wood. The state's firewood rules are on the page moving firewood in California, and where reports go in the United States is on reporting a pest in the United States.

Management as the sources list it

UC IPM says human-assisted movement of infested cut wood is the biggest threat for spreading the borer, that wood cut and kept on site for two years should be free of live borers, and that options exist for treating wood that has to move. It says insecticide testing was under way and that treatments are more likely to protect healthy trees than save heavily infested ones. CDFA says trap lures tested were not effective, and Purdue names purple prism traps without a lure as an approved survey method. This page gives no product names, rates or timings. For who may apply pesticides, see pesticide licences.