Goldspotted oak borer

The Goldspotted oak borer (Agrilus auroguttatus) is a destructive wood-boring beetle of the family Buprestidae (metallic wood-boring beetles). Originally native to parts of Mexico and Arizona, it has become a significant invasive threat to oak ecosystems, particularly in regions where it has been accidentally introduced.

This beetle primarily targets oak species (Quercus), showing a strong preference for coast live oak, canyon live oak, and California black oak. In infested areas, the pest can cause extensive mortality, leading to the loss of large, ecologically vital trees that define the landscape.

The life cycle of the beetle is closely tied to the host tree's physiology. Adults emerge in the summer to mate and lay eggs on the bark. Upon hatching, the larvae bore through the bark to feed on the phloem and cambium layers. This larval feeding disrupts the transport of water and nutrients, effectively girdling the tree and causing its decline over one to several years.

Monitoring for signs of infestation is crucial for early detection. Key indicators of the presence of the Goldspotted oak borer include:

• D-shaped exit holes on the surface of the bark.
• Thinning and dieback of the tree canopy.
• Staining or dark, wet-looking patches on the trunk caused by sap flow.
• Presence of larval galleries underneath the outer bark.

Management strategies focus on containment and sanitation. The most effective way to slow the spread is to restrict the movement of infested firewood or timber. Once an oak is confirmed to be heavily infested, removal and disposal (chipping or burning) of the wood are recommended to reduce the population of emerging adults. Insecticide treatments are sometimes used for high-value individual trees as a preventative measure.