Goldspotted Oak Borer in California: Invasion History, Biology, Impact, Management, and Implications for Mediterranean Forests Worldwide

Abstract

In 2008, the goldspotted oak borer, Agrilus auroguttatus Schaeffer (Coleoptera: Buprestidae), was first linked to elevated levels of oak mortality in southern California (CA), but it appears to have impacted oak woodlands and mixed conifer forests across all land ownerships in this region for nearly two decades. This unexpectedly damaging indigenous exotic phloem- and wood-boring pest is hypothesized to have been introduced in the late 1990s to early 2000s via infested firewood from southeastern Arizona to San Diego County, CA. The life history and impact of A. auroguttatus on oaks were unknown in its native range prior to 2008, and confusion surrounding its taxonomic placement further complicated the status of this emerging pest problem. The primary tree species infested in CA are coast live oak, Quercus agrifolia Nee, and California black oak, Quercus kelloggii Newb. As the invaded range expands, A. auroguttatus may interact with the broader community of other exotic and native pests of oaks in CA and continue to cause ecological and economic impacts. Early detection of A. auroguttatus is an imperative prerequisite for managing this invasive species and preventative and suppression treatments have been developed to protect high-value oaks. The movement of infested firewood will likely result in additional satellite infestations across the range of susceptible hosts from Baja California Norte, Mexico to southern Oregon. Agrilus auroguttatus currently represents the most significant insect threat to oaks in CA, but, if they are introduced, other European and eastern North American Agrilus species also threaten these Mediterranean forest ecosystems.