Forest Insect

& Disease

Leaflet 183

Revised August 2017

U.S. Department of Agriculture • Forest Service

Goldspotted Oak Borer

T.W. Coleman1, M.I. Jones2, S.L. Smith3, R.C. Venette4, M.L. Flint5, and S.J. Seybold6

New Mexico, and southwestern Texas. 

Specimens of GSOB have only been 

collected from Arizona, California, 

and Mexico. In southeastern Arizona, 

GSOB feeds primarily on Q. emoryi, 

and silverleaf oak, Q. hypoleucoides A. 

Camus (both Section Lobatae). Larval 

feeding injures the phloem and outer 

xylem of these red oak species, with 

most feeding activity and occasional 

cases of tree mortality noted in largeThe goldspotted oak borer (GSOB), 

Agrilus auroguttatus Schaeffer 

(Coleoptera: Buprestidae) (Figure 

1), is a flatheaded phloem- and wood 

borer that infests and kills several 

species of oak (Fagaceae: Quercus) in 

California. One or more populations 

of GSOB were likely introduced via

infested firewood into San Diego 

County, California from the native 

range in southeastern Arizona. Since 

its introduction to California, GSOB 

has expanded its range and has killed 

red oaks (Quercus Section Lobatae) 

nearly continuously across public and 

private lands (Figure 2).

Distribution and Hosts

The native distribution of GSOB likely 

coincides with that of Emory oak, Q. 

emoryi Torrey, including the Coronado 

National Forest in southeastern 

Arizona and floristically related 

regions in northern Mexico, southern 

1

Entomologist, USDA Forest Service, Forest Health Protection, San Bernardino, CA; 

2

Entomologist, Dept. of Environmental Science and Forestry, Syracuse University, 

Syracuse, NY; 3Entomologist, USDA Forest Service, Forest Health Protection, 

Susanville, CA; 4Research Biologist, USDA Forest Service, Northern Research Station, 

St. Paul, MN; 5

Entomologist, Dept. of Entomology and Nematology and Statewide 

Integrated Pest Management Program, University of California, Davis, CA; 6Research 

Entomologist, USDA Forest Service, Pacific Southwest Research Station, Davis, CA.

Figure 1. Adult goldspotted oak borer, Agrilus 

auroguttatus, an exotic insect threatening red 

oaks in California (Adults are approximately 

0.35 inches long by 0.08 inches wide).
2

diameter trees [>17 inches in diameter 

at breast height (dbh)]. A sibling 

species, the Mexican goldspotted oak 

borer, A. coxalis Waterhouse, is native 

to central and southern Mexico and 

Guatemala, and was once synonymized 

with A. auroguttatus. Surveys have 

shown that Mexican GSOB feeds on 

both red oaks and white oaks (Section 

Quercus) in southern Mexico.

In 2004, GSOB was first detected in 

survey traps in southern California (San 

Diego Co.), but it was not linked to tree 

injury or mortality until 2008. In 2012, 

GSOB was detected in Riverside Co. 

and was likely introduced to this new 

county in infested firewood (Figure 2). 

The movement of infested firewood 

was also most likely responsible 

for additional satellite infestations 

of GSOB that have been detected 

elsewhere within San Diego Co., and 

in Orange Co. Unregulated movement 

of infested oak wood has presumably 

facilitated the dispersal of GSOB in 

southern California and will likely 

continue to play a role in its future 

dispersal in California and beyond.

In California, GSOB preferentially 

attacks and kills large-diameter coast 

live oaks, Q. agrifolia Née, and 

California black oaks, Q. kelloggii 

Newberry (>18 and 20 inches dbh, 

respectively). Interior live oak, Q. 

wislizeni A. DC., another red oak 

species, was susceptible to GSOB larval 

feeding in laboratory tests, but GSOB 

has not been observed to infest this oak 

species in the field. Goldspotted oak 

borer can also attack a taxonomically 

intermediate oak species, canyon live 

oak, Q. chrysolepis Liebm. (Section 

Protobalanus), and, on rare occasions, 

a white oak species, Engelmann oak, 

Q. engelmannii Greene, in California. 

Goldspotted oak borer has killed 

canyon live oak at low levels (<25% 

of surveyed trees) in San Diego Co. 

Figure 2. Aerially mapped oak mortality (red stippling) associated with the goldspotted oak 

borer in San Diego County in southern California (2002-2013). Disjunct infested areas (satellite 

populations indicated by ●) occur in San Diego County (San Diego); Riverside County (Idyllwild) 

and Orange County (Orange). 
3

Dead Engelmann oak trees have been 

observed with signs of GSOB injury 

(e.g., larval galleries and D-shaped 

emergence holes, see below), but tree 

mortality in these cases was likely a 

result of a complex of factors (e.g., 

drought and root disease). Several 

ornamental oak species, including 

holly oak, Q. ilex (Section Quercus), 

and cork oak, Q. suber (Section 

Cerris), are planted frequently in the 

urban areas of southern California and 

may be at risk. In laboratory studies, 

GSOB larvae fed on cork oak logs but 

were unable to complete development. 

However, it has been hypothesized that 

species in the Sections Quercus and 

Cerris are not favored by GSOB and 

likely not susceptible to the extensive 

injury needed to cause tree mortality.

In California, the range of coast live 

oak extends north from San Diego 

Co. along the Santa Anita Mountains 

and Transverse Mountain Range and 

then to northern California along 

the Coastal Mountain Range (Figure 

3). It also extends south into Baja 

California Norte, Mexico. California 

black oak occurs on Mt. Laguna and 

Palomar Mountain in San Diego Co., 

the Transverse Mountain Range, 

Coastal Mountain Range, and along 

the Sierra Nevada Mountain Range 

to southern Oregon. Goldspotted oak 

borer-caused mortality has occurred 

in coast live oak at sea level as well as 

in California black oak at elevations 

up to approximately 6,000 feet in 

San Diego Co.; in laboratory tests, 

prepupae (mature larvae in a hair-pin 

configuration) have shown a coldtolerance of approximately -0.4° F 

during the winter months. The beetle’s 

distribution will likely expand from 

San Diego, Riverside, and Orange Cos. 

to mirror the range of its primary hosts 

and conducive climatic conditions in 

California and into Oregon and Mexico 

(Figure 3).

Figure 3. Potential range of goldspotted oak borer in Arizona, California, New Mexico, Oregon, 

and Baja California Norte, Mexico based on host distributions and climatic suitability. On the map, 

areas with hosts are colored, and climatically suitable areas within the distribution of hosts appear 

as shades of yellow (moderately suitable), orange, and red (highly suitable). 
4

the main stem is girdled and the 

oaks sustain significant injury and, 

eventually, mortality (Figure 4B). This 

process appears to be gradual, taking 

from 3 to 5 years. However, oaks 

predisposed by other injury agents 

(e.g., drought and root disease) may 

succumb more quickly to the effects of 

GSOB larval feeding.

In coast live oak woodlands in eastern 

San Diego Co. where trees have 

suffered at least a decade of infestation 

from GSOB, oak mortality levels have 

approached 45%. Infestation rates have 

been high (>90%) on large-diameter 

oaks at the hypothetical origin of the 

beetle’s introduction near Descanso 

and Guatay in San Diego Co., but the 

rates are lower (<10%) at the edges of 

the advancing infestation.

The expansion of the core area infested 

by GSOB has progressed slowly in 

San Diego Co. despite a maximum 

adult flight distance of approximately 

0.9 miles in tethered flight mill assays 

in the laboratory. Moderately and 

severely infested trees (known as 

brood trees) represent <7% of the 

oaks in forest stands in areas that have 

Figure 4. Typical goldspotted oak borer larval feeding galleries under recently removed bark of a 

living coast live oak tree (A) and etched on the xylem (wood) surface of a dead coast live oak tree 

(B). The meandering dark-colored galleries in living phloem and xylem (A) are characteristic of 

goldspotted oak borer larval feeding.

Impacts

Neither GSOB nor Mexican GSOB is 

considered a significant pest or threat 

to forest health in its native range. 

Instead, they have caused minor levels 

of injury to oaks (4% infestation 

rates) and have been associated with 

background levels of tree mortality in 

Arizona (2%) and Mexico (1%). As 

a consequence, virtually no research 

related to the biology and ecology of 

these species occurred prior to 2008 

when GSOB-caused oak mortality was 

discovered in California. 

The death of large-diameter coast 

live oaks and California black oaks in 

California results from several years of 

extensive larval feeding at the interface 

of the phloem and xylem (Figure 4). 

This feeding kills large sections of 

live tissue (Figure 4A), including the 

vascular cambium. As a consequence, 

A

B
5

been infested for longer than a decade. 

Coast live oak brood trees were 

also found at low densities in newly 

infested sites and, based on inferred 

population density from emergence 

hole records, they contain 66 to 93% 

of the GSOB population at these 

sites. The contrast between the rate of 

spread of the core population and the 

appearance of satellite populations in 

Orange, Riverside, and San Diego Cos. 

suggests that GSOB will spread slowly 

via natural dispersal or quickly via

human-assisted dispersal (Figure 2).

Life History

The goldspotted oak borer typically 

completes one generation in a year. 

However, anecdotal evidence suggests 

that populations may require more than 

one year to complete development in 

healthier hosts. In southern California, 

adults fly from mid-May to early 

October with peak flight occurring in 

late-June to early July (Table 1A). The 

majority of adult flight occurs from 

June to September. Adults can live for 

several months in the laboratory, but 

longevity has not been recorded in the 

field and is likely shorter in duration. 

Adults feed on oak foliage to survive, 

and females require approximately 10 

days of feeding to become sexually 

mature and likely mate in the crown or 

on the bark surface of the main stem 

or larger branches. In the laboratory, 

a single female can lay approximately 

200-500 eggs. Females lay eggs in 

fissures and crevices on the bark surface 

of the main stem and larger branches, 

either singly or in clusters (Figure 5). 

The eggs are oval, approximately 0.01 

inches wide, tan-colored, and very 

difficult to find on the bark surface. 

Eggs develop in approximately 12 days 

and first instar larvae bore through the 

bark into the phloem. 

Figure 5. Goldspotted oak borer eggs laid on 

the bark surface of coast live oak.

Table 1. Approximate timing of the goldspotted oak borer life cycle in southern California (A) and 

optimal timing of trapping period (B); application of contact (C) and systemic insecticides (D); and 

timing of mechanical grinding (E) and tarping (F) of infested oak wood.
6

Figure 6. A goldspotted oak borer first instar larva (A), fourth instar larva (B), mature larva/

prepupa (C), constricted larva/prepupa (D), pupa (E), and adults (F). The second arrow depicts 

the location of the ventral longitudinal groove on the abdomen of males. 

A B C D E

Goldspotted oak borer larvae likely 

complete four instars. Larvae are 

white, legless, and approximately 0.8 

inches long by 0.1 inches wide when 

fully mature. First instar larvae are 

<0.05 inches long and difficult to locate 

in the phloem (Figure 6A). Larvae 

have C-shaped spiracles (holes where 

air exchange occurs) and a pair of 

spines at the tip of the abdomen, both 

of which can be used to identify all 

Agrilus larvae (Figure 6B). In southern 

California, larvae can be found feeding 

from July to mid-December in the 

phloem and primarily on the outer 

xylem surface (Table 1A). Mature 

larvae migrate to the outer phloem just 

beneath the bark where they create a 

pupal cell and form a prepupa (Figure 

6C,D). Prepupae have been found in 

the outer phloem nearly year round, 

but at higher densities during the cooler 

months (November to May) (Table 1A). 

Ground surveys and sampling of trees 

for live GSOB should be conducted at 

this time of year because mature larvae 

(prepupae) can be observed easily in 

the outer phloem (Figure 7). 

Immediately prior to pupation, larvae 

begin to constrict to adult length in 

the pupal cell (Figure 6D). Pupae 

and teneral (newly formed) adults 

are present from April to August in 

the pupal cells. Pupae are the same 

size as adults, but initially are white 

and soft-bodied (Figure 6E). Pupae 

transform into teneral adults when 

their exoskeleton begins to sclerotize, 

or harden, and darken in color.

Adults are black to dark green with 

three dorsal pairs of gold-colored 

pubescent spots on the elytra and one 

faint pair located dorsolaterally on the 

thorax (Figures 1 and 6F). Additional 

gold-colored pubescence is located 

laterally on the thorax and abdomen 

(Figure 1). Males can be differentiated 

from females by a ventral groove on the 

first male abdominal segment. Adults 

chew a D-shaped emergence hole 

through the outer bark and are seldom 

observed in the forest. Adults cause 

minor and barely noticeable feeding 

damage to oak foliage, which does not 

substantially impact tree health.

F
7

Figure 7. Goldspotted oak borer mature 

larva or prepupa can be found in the phloem 

adjacent to the bark surface of coast live oak. 

Figure 8. Goldspotted oak borer D-shaped 

emergence holes on the bark surface of coast 

live oak (A). High densities of emergence 

holes (marked in red paint, B) are observed 

frequently on coast live oak killed by 

goldspotted oak borer in California. 

Evidence of Infestation

Crown thinning and dieback are 

common indicators of declining oak 

health and typical of trees that are 

moderately and severely infested 

by GSOB. Newly infested trees 

may have healthy, full crowns, but 

thinning and dieback become evident 

following successive years of larval 

feeding. Crown color of coast live 

oak trees infested by GSOB or by the 

impact of various stress factors range 

from dark green (healthy) to grayish 

green (severely injured). Thinning 

crowns can be used to identify 

potentially infested trees for scrutiny 

for additional symptoms (see below). 

However, crown thinning does not 

always indicate GSOB infestation 

(e.g., distinct twig or branch mortality 

(flagging) in the crown can indicate 

injury by twig girdlers, bark beetles, or 

scale insects).

Goldspotted oak borer is the only 

subcortical insect that constructs 

D-shaped emergence holes on the main 

stem and larger branches (>8 inches in 

diameter) of oaks in California, making 

the presence of these holes a diagnostic 

sign of infestation by this exotic pest 

(Figure 8A).

A B

Unlike some other wood-boring 

Agrilus species, GSOB does not 

attack the upper branches in the crown 

during the early stages of infestation. 

The GSOB adult emergence holes 

(approximately 0.15 inches in 

diameter) can appear before any 

other injury symptoms are observed, 

but can be easily overlooked when 

they occur at low densities. A high 

density of emergence holes (10’s to 

1,000’s/8 feet of lower stem) on coast 

live oak and California black oak is 

not uncommon when trees have been 

infested for several years (Figure 8B). 

As the population density increases, 

emergence holes can be observed 

easily on the lower part of the main 

stem (<8 feet) of infested oaks. 

Thus, performing a total count of the 

emergence holes in this area of the 

stem can provide an estimate of the 

extent of GSOB injury.

B
8

Removing the outer bark and phloem 

exposes larvae and the signs of their 

feeding at the interface of the phloem 

and xylem. Larval galleries have 

a meandering pattern; are dark in 

color when the fresh bark is recently 

removed; are about 0.16 inches wide 

when larvae are mature; and are tightly 

packed with black boring dust (frass). 

Following infestation by GSOB, 

secondary wood borers, including other 

flatheaded borers, Chrysobothris mali 

Horn and Chrysobothris wintu Wellso 

and Manley (Coleoptera: Buprestidae), 

oak cordwood borers, Xylotrechus 

nauticus Mannerheim (Coleoptera: 

Cerambycidae), oak ambrosia 

beetles, Monarthrum spp. Kirsch and 

Gnathotrichus pilosus LeConte (both 

Coleoptera: Scolytidae), and western 

oak bark beetles, Pseudopityophthorus 

spp. Swaine (Coleoptera: Scolytidae), 

frequently attack these stressed oaks in 

southern California. Injury symptoms 

associated with these secondary insects 

can be mistaken for GSOB injury; see 

Flint et al. (2013) for a description of 

their emergence holes.

Dark-colored sap stains on the bark 

surface can indicate a GSOB-infested 

tree (Figure 9). Sometimes sap exudate 

over GSOB-infested areas can manifest 

as a blood-red secretion that hardens 

as it dries. Bark staining associated 

with GSOB injury is frequently 

observed along the main stem and 

larger branches, and is not associated 

with invaginations along the stem, at 

branch junctions, or mechanically and 

structurally wounded areas. Several 

secondary fungi can be associated with 

these dark-stained bark areas, but they 

are not always present on infested trees 

and may only occur after GSOB has 

already severely injured the tree.

Acorn woodpeckers, Melanerpes 

formicivorus Swainson (Piciformes: 

Picidae), forage for larvae, prepupae, 

and pupae just beneath the bark surface 

in the outer phloem. Woodpecker 

foraging occurs frequently from fall to 

early summer when larval densities are 

highest in these areas of the tree stem. 

Woodpeckers chip away the outer oak 

bark exposing the red phloem (in coast 

live oak) and the dark-colored larval 

galleries and pupal cells (Figure 10). 

The phloem exposed by woodpecker 

foraging turns black with age and thus 

becomes less evident over time. The 

degree of woodpecker foraging can 

vary greatly by site, but can be very 

extensive on heavily infested trees.

Figure 9. Dark-colored wet staining or red 

bleeding on the bark is sometimes associated 

with larval feeding by goldspotted oak borers. 

Bark staining does not always indicate 

goldspotted oak borer injury and may only 

appear after extensive injury has occurred. 

Figure 10 Woodpecker foraging for 

goldspotted oak borer prepupae on the main 

stem can expose larval galleries, pupal cells, 

and red phloem of coast live oak.
9

Management

Monitoring

Ground surveys are the most 

effective method for detecting GSOB 

infestations and determining the level 

of injury caused by GSOB. However, 

ground surveys are time consuming 

and GSOB-caused injury symptoms 

are often not obvious during the early 

stages of infestation. In its native 

range, rates of GSOB infestation and 

tree mortality are low (4% and 2%, 

respectively, in a forest stand). These 

rates have been much higher (90% 

and 45%, respectively) in the invaded 

range. Large-diameter red oaks are 

the preferred host and should be the 

focus of ground surveys. Furthermore, 

oaks along the forest stand edge should 

be checked first because there is an 

initial preference for GSOB to attack 

trees along the edges of a stand (<150 

feet from the forest stand edge). To 

facilitate detection of GSOB, the outer 

bark of heavily infested trees should be 

chipped away to expose prepupae and 

pupae in the outer phloem or the black 

meandering larval galleries on the 

xylem surface. Tree injury symptoms 

caused by GSOB, including the degree 

of crown thinning; density of D-shaped 

emergence holes and bark staining; and 

the presence/absence of woodpecker 

foraging, have been integrated into a 

system to rank tree health and guide 

management decisions (Figure 11). 

Stickem-coated purple prism panel 

flight-intercept traps are the most 

effective traps for detecting GSOB 

(Figure 12). Traps should be monitored 

from May to September when most 

adult flight occurs (Table 1B). Traps 

should be positioned adjacent to the 

crowns of oaks on the southern aspect 

of a tree and hung at 9-10 feet. At 

sites with low population densities of 

GSOB (<20% infestation), the traps 

may be ineffective at detecting beetle 

populations.

Clear panel sticky traps placed at breast 

height on the main stem of declining 

oaks can also be used to capture GSOB 

adults. Felling live host oaks and 

leaving a high stump (approximately 4 

feet tall) can serve as a trap “tree” for 

GSOB. Girdling live oak trees has not 

been very effective at attracting GSOB 

even at sites with high beetle population 

densities (>50% infestation). These 

methods can be useful for detecting 

GSOB, but are not efficacious tools for 

preventing or suppressing infestations. 

Goldspotted oak borer adults have 

responded to host bark and foliage 

volatiles in electroantennographic 

detection analyses in the laboratory; 

however, a lure to improve GSOB 

adult trap catches has not yet been 

developed. Like most Agrilus spp. 

studied so far, GSOB does not respond 

to ethanol-baited traps. However, 

additional research will be necessary 

to determine whether ethanol may be 

a semiochemical utilized by GSOB 

in the context of other host- or beetleproduced signals.

Although the traps described here have 

been useful for researchers or managers 

to detect movement of GSOB into new 

areas, they are not sensitive enough 

to guide management decisions. 

Land managers should focus their 

monitoring efforts on surveying for 

GSOB emergence holes on oak trees 

and ground-checking declining and 

recently killed oaks as indicated from 

aerial survey data.
10

Figure 11. A health rating system developed to determine the degree of goldspotted oak borer 

injury and assist with management decisions (modified from Hishinuma et al. 2011). The health 

rating system includes the degree of crown thinning and dieback; the density of D-shaped 

emergence holes and areas of bark staining; and presence/absence of woodpecker foraging.

1- CROWN RATING (1-5)

2- EMERGENCE HOLE RATING (1-3) 3- BARK STAINING RATING (1-4)

4- WOODPECKER FORAGING (+/-)

1: Full, healthy crown (0% leaf loss); 2: Minor twig dieback and/or light thinning (10-25% leaf loss); 

3: Moderate twig dieback and thinning (25-50% leaf loss); 4:Severe dieback to larger branches (>50% leaf 

loss); 5: Tree is dead, no living foliage.

1: Less than ten D-shaped emergence holes on the 

lower main stem (<8 feet). 2: Ten to 25 emergence 

holes. 3: Greater than 25 emergence holes.

1: One to five areas of staining on the lower 

main stem (<8 feet). 2: Six to ten stained areas. 

3: Greater than 10 areas stained areas. 4: Bark 

cracking evident.

Present or absent on the main stem or larger branches

1

3 4

2
11

Insecticide Treatments

A contact insecticide applied to the 

main stem and to the larger branches 

(>8 inches in diameter) is the best 

option for preventing GSOB injury to 

high-value oaks. To reduce the amount 

of spray drift and the impact to nontarget arthropods, treating the entire 

crown is not suggested and likely not 

feasible for ground applications to 

large oaks. Contact spray applications 

should occur in May prior to the adult 

flight period in southern California and 

be re-applied annually by a certified 

pesticide applicator (Table 1C). These 

preventive insecticides should only 

be applied after evidence of GSOB 

has been found in the immediate area 

(<1⁄2 mile). Contact sprays or systemic 

insecticides (see below) should not 

be applied to GSOB-infested oaks 

with a crown injury rating of “3” or 

greater and an emergence hole rating 

of “3” (>25 emergence holes, see 

Figure 11) because they have already 

experienced high levels of injury. In 

these instances, insecticide treatments 

may have limited benefit in preventing 

tree mortality. Trees with >120 GSOB 

emergence holes on the lower stem 

(<8 feet) will likely die in the next 

few years. Preventive contact sprays 

of a carbamate (Sevin) or a pyrethroid 

(bifenthrin and permethrin) insecticide 

have killed GSOB adults in laboratory 

assays of treated foliage one month and 

one year post-application.

Systemic insecticides applied as a 

trunk injection or a basal spray may 

kill larvae feeding in the phloem 

and outer xylem, but they may also 

target adults when they feed on the 

foliage. These materials should also 

be applied by a certified pesticide 

applicator. Systemic insecticides such 

as neonicotinoids (e.g., imidacloprid) 

or emamectin benzoate were effective 

at killing adults in laboratory leaffeeding bioassays when leaves were 

collected from coast live oaks and 

smaller diameter California black oaks 

that had been injected in December 

and/or February and assayed 3 or 5 

months later. In the field, systemic 

treatments with imidacloprid or 

emamectin benzoate slowed the rate of 

growth of GSOB populations on large 

diameter coast live oaks. However, 

studies to evaluate protection of trees 

from GSOB with systemic insecticides 

are still in progress. Insecticide 

uptake was greater in smaller diameter 

California black oaks than coast live 

oaks with stem-injected applications. 

Systemic treatments applied as trunk 

injections to oaks should be applied 

from November to February when 

treatment can be followed by seasonal 

precipitation, which facilitates 

translocation of the active ingredient in 

the vascular system (Table 1D).

Basal spray applications of a systemic 

insecticide (dinotefuran) to uninfested 

coast live oak and California black 

Figure 12. A purple prism panel flightintercept trap hung at 9-10 feet on a metal 

conduit pole adjacent to the crown of a coast 

live oak for monitoring the flight of goldspotted 

oak borer adults.
12

oak trunks resulted in high levels of 

active ingredient in foliage samples 

when applied in May just prior to 

adult flight. The active ingredient 

had declined dramatically when 

foliage was collected in September. 

Basal trunk applications to coast live 

and California black oaks yielded 

the greatest translocation of active 

ingredient in smaller diameter (<12 

inches dbh) trees, but translocation 

was also detected in foliage at high 

levels one-month post application in 

large diameter (>40 inches dbh) trees. 

Although GSOB adults were not killed 

in laboratory leaf-feeding bioassays, 

the highest label rate was not used in 

these studies. Based on best current 

knowledge, we recommend that basal 

trunk applications of dinotefuran 

be applied annually, whereas trunkinjected applications of imidacloprid 

and emamectin benzoate be applied 

once every two years in southern 

California. Repeated stem injections 

can cause injury to the trunk, and treated 

trees should be monitored for bark 

cracking, staining, and crown thinning. 

Watering high-value oaks can facilitate 

insecticide uptake and alleviate 

drought stress during dry years. For 

high-value sites or individual trees, a 

combination of topical and systemic 

insecticide treatments may provide the 

most effective protection. However, 

this combined insecticidal approach 

has not been evaluated sufficiently to 

support this management action.

Mechanical Treatments

Grinding GSOB-infested wood to 

a particle size of <3 inches with a 

3-inch-“minus” grinding screen is the 

most effective mechanical method for 

eliminating GSOB populations (Figure 

13A). For greatest impact on GSOB 

population density and dispersal, 

grinding wood should occur before the 

emergence of adults in May, but the 

treatment can be applied year round 

to kill any of the life stages (Table 

1E). Grinding wood is only practical 

for large-scale management projects, 

due to the specialized equipment 

required and the cost of the equipment. 

Chipping infested wood is not 

recommended as a management option 

because of the difficulty with treating 

large, dense pieces of oak stems with 

a standard chipper. Goldspotted oak 

borer does not attack the smaller 

stems and branches, which are often 

targeted in chipping operations. A 

more economical and feasible option 

for landowners with small quantities of 

wood is to either enclose or debark the 

infested wood (Figure 13B,C). 

Figure 13. To manage wood infested with 

goldspotted oak borer, large quantities of wood 

can be ground with a tub grinder (A); small 

quantities of wood can be enclosed with plastic 

sheeting (B); or small quantities of wood can 

be debarked by landowners (C). If used for 

firewood, the wood should be burned locally.

A

B C
13

Stacks of infested firewood can be 

enclosed with thick (6 mil), clear, UV 

resistant plastic sheeting and placed in 

a sunny location from the first of May 

to September (Table 1F). If the edges 

of the tarp are buried in the soil and 

the integrity of the tarp is maintained 

from May to September, emerging 

adults are not capable of escaping and 

will eventually die. Metal screening, 

tightly rolled and secured at the seams, 

can also be used to enclose wood. 

Debarking wood requires the manual 

separation of the bark and phloem 

from the wood prior to the emergence 

of GSOB adults. A log splitter, or other 

debarking tools, can remove outer bark 

in large pieces. This option can be very 

labor intensive and is only feasible for 

small quantities of wood. Goldspotted 

oak borers can survive in the bark and 

phloem shavings, so this material must 

be destroyed (e.g., ground or burned) 

or tarped to eliminate all live beetles.

Cultural Treatments

Removing moderately- and severelyinfested trees (i.e., “brood” trees) may 

slow GSOB population growth at highvalue sites. These infested trees should 

be felled and the wood managed 

by using one of the aforementioned 

mechanical treatments. Felling 

infested trees and the application 

of a preventive insecticide to any 

remaining uninfested or lightly 

infested (<10 emergence holes) largediameter oaks may provide the best 

opportunity for maintaining high-value 

sites. However, no experimental data 

are available presently to support these 

combined management steps.

Limiting the movement of GSOBinfested wood into and within a 

community may be the most effective 

management method for reducing 

GSOB-associated tree mortality. In 

mountain communities, firewood 

is often a valuable commodity and 

sometimes the primary source of 

heating. To minimize movement or 

introduction of GSOB, the following 

simple and effective approaches 

for reducing GSOB-associated tree 

mortality are available: 1) educate 

community members to screen 

incoming firewood for evidence of 

GSOB; 2) allow wood from recently 

felled trees to season within the 

infested zone for longer than two years; 

and 3) keep infested material away 

from uninfested trees. Limiting the 

movement of firewood <50 miles from 

the location of harvest, (e.g., “Buy it 

where you burn it” approach) is a best 

management practice for limiting the 

spread of GSOB and other subcortical 

invasive insects.

Natural Enemies

Three parasitoid wasp species and 

several generalist insect predators 

have been associated with GSOB in 

Arizona and California. The impact 

of these parasitoids and predators on 

GSOB populations is unknown in 

both regions, but low levels of GSOB 

mortality (<15%) have been attributed 

to some of these species. Low densities 

of natural enemies and low levels of 

host resistance may have contributed 

to the elevated levels of oak mortality 

by this indigenous exotic species in 

California. Calosota elongata Gibson 

(Hymenoptera: Eupelmidae), a newly 

described ectoparasitoid wasp, is 

only known from GSOB prepupae 

in Arizona and California (Figure 

14A,B). Calosota elongata was likely 

introduced into California with the 

original GSOB population, but its 

known adventive distribution is limited 

to southeastern San Diego Co. in 
14

California. A Trichogramma sp. wasp 

(Hymenoptera: Trichogrammatidae) 

was associated with GSOB eggs in 

Arizona, but was only found at low 

densities there and is believed to be 

a generalist parasitoid (Figure 14C). 

Atanycolus simplex (Hymenoptera: 

Braconidae) is a generalist larval 

parasitoid found in association with 

GSOB, but it also parasitizes other 

wood-boring insects throughout the 

USA (Figure 14D). The straw itch 

mite, Pyemotes tritici Lagrèze-Fossat 

and Montané (Acari: Pyemotidae), has 

been found on prepupae, pupae, and 

unemerged GSOB adults from Arizona 

and California and on Mexican GSOB 

in southern Mexico (Figure 14E). 

Pyemotes tritici has a cosmopolitan 

distribution and parasitizes species in 

several insect orders, including beetles 

(Coleoptera), moths (Lepidoptera), 

and ants (Hymenoptera). Snakeflies 

(Raphidioptera) and bark-gnawing 

beetles (Trogossitidae) have also 

been found feeding on GSOB larvae 

or in larval galleries. Though it has 

appeared to be locally extensive on 

highly infested trees, the impact of 

woodpecker feeding on GSOB has not 

been quantified. In general, the impact 

of insect and avian predators on GSOB 

population density is likely to be limited 

in California. Calosota elongata was 

considered a promising candidate for 

augmentative biological control in 

California. However, the difficulty of 

rearing GSOB populations on cut logs 

and at high densities in a laboratory 

setting makes an augmentative 

biological control program infeasible 

at this time. 

Assistance

If you suspect that you have found signs 

of GSOB or symptoms of its damage on 

your property, or on municipal, state, 

or federal lands please contact a Pest 

Control Advisor, your local University 

Cooperative Extension Office, the 

County Agricultural Commissioner’s 

Office, or your local USDA Forest 

Service, Forest Health Protection 

representative (http://www.fs.fed.us/

foresthealth/). This publication and 

other Forest Insect and Disease Leaflets 

are available online (www.fs.usda.gov/

goto/fhp/fidls).

Acknowledgements

The authors thank D. Betancourt, A. 

Cipollone, A.D. Graves, Z. Heath, K. 

Koeslag, J. Lydick, J. Moore, and G. 

Walter (USDA Forest Service, Forest 

Health Protection); B. Strom (USDA 

Forest Service, Southern Research 

Figure 14. Natural enemies associated with 

goldspotted oak borer, include Calosota 

elongata (A: parasitoid larvae feeding on a 

GSOB prepupa and B: adult parasitoids); 

Trichogramma sp. adult wasp on a GSOB 

egg (C); Atanycolus simplex adult wasp (D); 

and the straw itch mite, Pyemotes tritici on a 

GSOB prepua (E).

A B

C D

E
15

Station); Y. Chen, L. Haavik, S.M. 

Hishinuma, and A. Poloni (Dept. of 

Entomology, University of California, 

Davis); M. Hoddle, V. Lopez, and R. 

Stouthamer (Dept. of Entomology, and 

Nematology, University of California, 

Riverside); L. Singleton (Dept. of 

Biological Sciences, California State 

University, Long Beach), and D. Crook 

(Dept. of Entomology, University 

of Massachusetts) for contributing 

information and resources to the 

information presented in this leaflet. 

We appreciate critical reviews of this 

leaflet by Y. Chen, R.A. Haack (USDA 

Forest Service, Northern Research 

Station), S.M. Hishinuma, and A.S. 

Munson (USDA Forest Service, Forest 

Health Protection).

Photo Credits

Figure 2: J. Moore (USDA Forest Service, 

Forest Health Protection); Figure 3: R. Venette 

(USDA Forest Service, Northern Research 

Station); Figure 14C: R. Lara (University of 

California, Riverside); All other figures by T.W. 

Coleman (USDA Forest Service, Forest Health 

Protection).

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html
16

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Published by USDA Forest Service, Pacific Northwest Region (R6), Portland, Oregon

FS/R6/RO/FIDL#183-15/001 (Rev. 08/2017

Pesticides used improperly can be injurious to humans, animals, and plants. Follow the directions and heed all precautions on the 

labels. Some States have restrictions on the use of certain pesticides. Check your state and local regulations. Also, because pesticides 

are under constant review by the Federal Envioronmental Protection Agency, consult your county agricultural agent or State extension 

specialist to be sure the intended use is still registered.

Haavik, L.J., T.W. Coleman, Y. Chen, M.I. Jones, 

R.C. Venette, M.L. Flint, and S.J. Seybold. 2012. 

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