Agrilus coxalis
Encyclopedia
Agrilus coxalis is a species of jewel beetle known by the common name goldspotted oak borer. It is a woodboring beetle
best known for destroying stands of oak trees
in the Cleveland National Forest
in San Diego County, California
, in the United States.
Significant oak mortality was noted in the area starting in 2002 near Descanso, California
. It was thought that drought
was causing the decline until surveys revealed evidence of damage to healthy trees. On investigation it was determined that the agent causing the damage was Agrilus coxalis, a beetle
not previously noted in the area. The tree species most affected are the coast live oak (Quercus agrifolia) and California black oak (Quercus kelloggii). The canyon live oak
(Quercus chrysolepis) and silverleaf oak (Quercus hypoleucoides) are also affected. The insect was first seen in the region in 2004 at Cuyamaca Rancho State Park
, and it was confirmed to be the cause of oak damage in 2008 when adults and larva
e were collected from the host trees.
Little is known about the life history of the insect, whether it is introduced
or moving into the area as part of a natural range expansion, or its current distribution. The beetle has been found in Guatemala
, Mexico
, and Arizona
, but it has never been known to cause this sort of oak destruction. However it is thought that the beetle in Arizona is a separate species from the one in Central America, Agrilus auroguttatus
.
Since dead oaks were first seen near Descanso, damage was found on 67% of oaks examined in surveys, and about 13% of the trees were dead. The affected region is an area 50 by 40 kilometers mostly within National Forest
boundaries in the Peninsular Ranges
east of San Diego
. Damage from the beetle takes the form of blackened larval feeding galleries revealed in the wood when woodpecker
s remove bark, red and black staining on the bark that occurs when sap
drains from damaged phloem
, thinning grayish crowns on injured trees, and dead twigs and branches. The adult leaves D-shaped exit holes on the outside of the tree.
Initially, it was estimated that 15,000 individual trees have been killed by this pest. On September 3, 2011, the San Diego Union-Tribune published a correction of this estimate by UC Riverside researchers that puts the number at 80,000 trees killed. Dead trees increase the likelihood and severity of wildfire
in this already highly fire-prone area.
The adult gold spotted oak borer is dull dark metallic green in color with three characteristic yellow spots on each forewing
. It is about a centimeter long. The larva is white and legless and reaches 18 millimeters in length.
Current research is aimed toward locating a predator or parasitoid
that preys on the beetle larvae, but will not have serious impact on other native species. Until further study yields suggestions for the management of this pest insect, the US Forest Service
advises forestry workers to use containment guidelines now in practice for the control of similar jewel beetle pests, such as the emerald ash borer
and bronze birch borer
. If the beetle was introduced to the area, it may have come in on firewood
. Scientists advise against transporting oak wood since it may spread the pest.
Woodboring beetle
The term woodboring beetle encompasses many species and families of beetles whose larval or adult forms eat and destroy wood . Larval stages of some are commonly known as woodworms.-Invasion and control:...
best known for destroying stands of oak trees
Oak
An oak is a tree or shrub in the genus Quercus , of which about 600 species exist. "Oak" may also appear in the names of species in related genera, notably Lithocarpus...
in the Cleveland National Forest
Cleveland National Forest
Cleveland National Forest encompasses 460,000 acres , mostly of chaparral, with a few riparian areas. A warm dry mediterranean climate prevails over the Forest. It is the southernmost National forest of California. It is administered by the United States Forest Service, a government agency within...
in San Diego County, California
San Diego County, California
San Diego County is a large county located in the southwestern corner of the US state of California. Hence, San Diego County is also located in the southwestern corner of the 48 contiguous United States. Its county seat and largest city is San Diego. Its population was about 2,813,835 in the 2000...
, in the United States.
Significant oak mortality was noted in the area starting in 2002 near Descanso, California
Descanso, California
Descanso is a small census-designated place in the Mountain Empire area of southeastern San Diego County, California and part of California's 52nd congressional district. Descanso is located east of Alpine and west of Pine Valley. The population was 1,423 at the 2010 census.The community's name...
. It was thought that drought
Drought
A drought is an extended period of months or years when a region notes a deficiency in its water supply. Generally, this occurs when a region receives consistently below average precipitation. It can have a substantial impact on the ecosystem and agriculture of the affected region...
was causing the decline until surveys revealed evidence of damage to healthy trees. On investigation it was determined that the agent causing the damage was Agrilus coxalis, a beetle
Beetle
Coleoptera is an order of insects commonly called beetles. The word "coleoptera" is from the Greek , koleos, "sheath"; and , pteron, "wing", thus "sheathed wing". Coleoptera contains more species than any other order, constituting almost 25% of all known life-forms...
not previously noted in the area. The tree species most affected are the coast live oak (Quercus agrifolia) and California black oak (Quercus kelloggii). The canyon live oak
Quercus chrysolepis
Quercus chrysolepis, commonly termed Canyon Live Oak, or Golden Cup Oak, is a species of evergreen oak that is found in the southwestern part of North America, notably in the California Coast Ranges. This tree is often found near creeks and drainage swales growing in moist cool microhabitats...
(Quercus chrysolepis) and silverleaf oak (Quercus hypoleucoides) are also affected. The insect was first seen in the region in 2004 at Cuyamaca Rancho State Park
Cuyamaca Rancho State Park
Cuyamaca Rancho State Park is a state park located forty miles east of San Diego, California in the Laguna Mountains of the Peninsular Ranges. The park's 26,000 acres feature pine, fir, and oak forests, with meadows and streams that exist due to the relatively high elevation of the area compared...
, and it was confirmed to be the cause of oak damage in 2008 when adults and larva
Larva
A larva is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle...
e were collected from the host trees.
Little is known about the life history of the insect, whether it is introduced
Introduced species
An introduced species — or neozoon, alien, exotic, non-indigenous, or non-native species, or simply an introduction, is a species living outside its indigenous or native distributional range, and has arrived in an ecosystem or plant community by human activity, either deliberate or accidental...
or moving into the area as part of a natural range expansion, or its current distribution. The beetle has been found in Guatemala
Guatemala
Guatemala is a country in Central America bordered by Mexico to the north and west, the Pacific Ocean to the southwest, Belize to the northeast, the Caribbean to the east, and Honduras and El Salvador to the southeast...
, Mexico
Mexico
The United Mexican States , commonly known as Mexico , is a federal constitutional republic in North America. It is bordered on the north by the United States; on the south and west by the Pacific Ocean; on the southeast by Guatemala, Belize, and the Caribbean Sea; and on the east by the Gulf of...
, and Arizona
Arizona
Arizona ; is a state located in the southwestern region of the United States. It is also part of the western United States and the mountain west. The capital and largest city is Phoenix...
, but it has never been known to cause this sort of oak destruction. However it is thought that the beetle in Arizona is a separate species from the one in Central America, Agrilus auroguttatus
Agrilus auroguttatus
Agrilus auroguttatus is a species of jewel beetle in the United States.It was considered a subspecies of Agrilus coxalis Waterhouse 1889, but now it is regarded as a separate species. Much of what is on the A. coxalis page refers to this species. Coleman and Seybold reported that A. auroguttatus...
.
Since dead oaks were first seen near Descanso, damage was found on 67% of oaks examined in surveys, and about 13% of the trees were dead. The affected region is an area 50 by 40 kilometers mostly within National Forest
United States National Forest
National Forest is a classification of federal lands in the United States.National Forests are largely forest and woodland areas owned by the federal government and managed by the United States Forest Service, part of the United States Department of Agriculture. Land management of these areas...
boundaries in the Peninsular Ranges
Peninsular Ranges
The Peninsular Ranges are a group of mountain ranges, in the Pacific Coast Ranges, which stretch from southern California in the United States to the southern tip of Mexico's Baja California peninsula; they are part of the North American Coast Ranges that run along the Pacific coast from Alaska...
east of San Diego
San Diego, California
San Diego is the eighth-largest city in the United States and second-largest city in California. The city is located on the coast of the Pacific Ocean in Southern California, immediately adjacent to the Mexican border. The birthplace of California, San Diego is known for its mild year-round...
. Damage from the beetle takes the form of blackened larval feeding galleries revealed in the wood when woodpecker
Woodpecker
Woodpeckers are near passerine birds of the order Piciformes. They are one subfamily in the family Picidae, which also includes the piculets and wrynecks. They are found worldwide and include about 180 species....
s remove bark, red and black staining on the bark that occurs when sap
Sap
Sap may refer to:* Plant sap, the fluid transported in xylem cells or phloem sieve tube elements of a plant* Sap , a village in the Dunajská Streda District of Slovakia...
drains from damaged phloem
Phloem
In vascular plants, phloem is the living tissue that carries organic nutrients , in particular, glucose, a sugar, to all parts of the plant where needed. In trees, the phloem is the innermost layer of the bark, hence the name, derived from the Greek word "bark"...
, thinning grayish crowns on injured trees, and dead twigs and branches. The adult leaves D-shaped exit holes on the outside of the tree.
Initially, it was estimated that 15,000 individual trees have been killed by this pest. On September 3, 2011, the San Diego Union-Tribune published a correction of this estimate by UC Riverside researchers that puts the number at 80,000 trees killed. Dead trees increase the likelihood and severity of wildfire
Wildfire
A wildfire is any uncontrolled fire in combustible vegetation that occurs in the countryside or a wilderness area. Other names such as brush fire, bushfire, forest fire, desert fire, grass fire, hill fire, squirrel fire, vegetation fire, veldfire, and wilkjjofire may be used to describe the same...
in this already highly fire-prone area.
The adult gold spotted oak borer is dull dark metallic green in color with three characteristic yellow spots on each forewing
Insect wing
Insects are the only group of invertebrates known to have evolved flight. Insects possess some remarkable flight characteristics and abilities, still far superior to attempts by humans to replicate their capabilities. Even our understanding of the aerodynamics of flexible, flapping wings and how...
. It is about a centimeter long. The larva is white and legless and reaches 18 millimeters in length.
Current research is aimed toward locating a predator or parasitoid
Parasitoid
A parasitoid is an organism that spends a significant portion of its life history attached to or within a single host organism in a relationship that is in essence parasitic; unlike a true parasite, however, it ultimately sterilises or kills, and sometimes consumes, the host...
that preys on the beetle larvae, but will not have serious impact on other native species. Until further study yields suggestions for the management of this pest insect, the US Forest Service
United States Forest Service
The United States Forest Service is an agency of the United States Department of Agriculture that administers the nation's 155 national forests and 20 national grasslands, which encompass...
advises forestry workers to use containment guidelines now in practice for the control of similar jewel beetle pests, such as the emerald ash borer
Emerald ash borer
The emerald ash borer is a green beetle native to Asia.In North America the borer is an invasive species, highly destructive to ash trees in its introduced range. The potential damage of this insect rivals that of Chestnut blight and Dutch Elm Disease...
and bronze birch borer
Bronze birch borer
The bronze birch borer Agrilus anxius is a wood-boring Buprestid beetle native to North America, more numerous in warmer parts of the continent and rare in the north. It is a serious pest on birch trees , frequently killing them...
. If the beetle was introduced to the area, it may have come in on firewood
Firewood
Firewood is any wood-like material that is gathered and used for fuel. Generally, firewood is not highly processed and is in some sort of recognizable log or branch form....
. Scientists advise against transporting oak wood since it may spread the pest.