The Mediterranean oak borer attacks the crown of a tree, killing limbs as the infestation grows, eventually infecting the trunk, and ultimately killing the tree. [Photo courtesy County of Marin]
An invasive beetle has penetrated the Marin County limits—and local agricultural watchdogs are on high alert.
The Mediterranean oak borer, an invasive insect that primarily feeds on white oaks, was recently detected in Novato. The Marin County Agricultural Commissioner is urging professional arborists and the public to keep an eye out for evidence of the invasive tree pest, which is native to Europe, the Middle East and North Africa.
The ambrosia beetle species is small—approximately 3 millimeters—and bores tunnels into stressed trees, specifically oaks. The beetles initially attack branches in the crown of a tree, killing limbs as the infestation grows. Eventually, the infestation spreads to the trunk and ultimately kills the tree. The insect was first detected in Napa County in 2019 and has since been found in nine counties.
The beetles carry and grow fungus in the galleries they bore; then they feed off the fungus, so they can live and reproduce within a tree for generations. Typically, the female beetles fly, but the males don’t.
Joe Deviney, Marin’s agricultural commissioner, said now that the oak borer is here, it’s likely here to stay.
“Education about the beetle is important, but unfortunately it can’t be eradicated and it’s becoming more widespread in our area,” Deviney said in a press announcement about the insect. “It was only a matter of time for the presence of this invasive pest to be confirmed in our county.”
Homeowners are urged to monitor tree crowns and, if they see a decline in leaf growth in one or more branches or observe other symptoms of an infestation, are encouraged to seek expert evaluation from a certified arborist. Learn more at mobpc.org.
