A new oak pest and vector of an oak wilt disease, Mediterranean oak borer (MOB) has become established in California and Oregon and is continuing to spread.
Mediterranean oak borer (MOB),
Xyleborus monographus, was found in Oregon for the first time in 2018 in Multnomah County. Another single specimen was found in Marion County in 2021. Since then, specimens have been found in Clackamas and Washington Counties. MOB is a European species of ambrosia beetle that was first collected in California in 2017 in the Napa area, where it is damaging multiple species of oaks. It is a vector of an oak wilt,
Raffaelea montetyi.
Experiments have shown that Oregon white oak,
Quercus garryana, is susceptible to this oak wilt. Ambrosia beetles often have broad host ranges, and MOB has been found to attack many species including elm, maple, walnut, and others. It is believed that the beetles arrived in the US through European wine barrels, but they are most likely spreading within North America with the movement of firewood and green waste.
While it is unknown what MOB’s impact will ultimately be, it is causing increased oak mortality in both California and Oregon and represents a threat to North American oak species.