#21

The Mediterranean Oak Borer (MOB, Xyleborus monographus Coleoptera: Curculionidae: Scolytinae) a New Invasive Species Infesting Valley and Blue Oak in Northern California

Curtis Ewing, California Department of Forestry and Fire Prevention

Sheri Smith, USDA-FS, Region 5 and Michael Jones, UC-ANR, Lake County

The Mediterranean oak borer (MOB), Xyleborus monographus, is an invasive ambrosia beetle native to the Mediterranean region, including Europe, the Middle East, and North Africa, where it primarily attacks oak species. The first North American infestations of MOB were confirmed in valley oaks in Napa County, California in late 2019, followed by Lake and Sonoma Counties in early 2020, and Sacramento County in September 2020. MOB attacks at least 12 species of oaks in its native range. In California, it has been found infesting two species of white oak: most commonly valley oak and, to a lesser extent, blue oak. A single, very limited attack was found in a severely distressed California black oak. All ambrosia beetles (like MOB) grow fungi inside their galleries and use it as food for larvae and adults. Some of these fungi can be pathogenic and cause tree diseases that may lead to tree decline and, sometimes, tree death. Several species of fungi have been found associated with MOB in Napa County, and research is underway to determine if these fungi cause tree diseases. Oak trees infested with MOB are most easily identified by damage caused by the beetle’s tunneling activity (galleries) in the xylem. MOB galleries are often trellis-like, very crowded and intersecting, fan out in a single plane and 1.2-1.5 mm in diameter. Other signs and symptoms of MOB tunneling activity include boring dust in cracks of the tree bark, and sometimes oozing sap (“sap flux”). In addition to looking at the associated pathogens, cooperative work is also ongoing to 1) provide information regarding the origin, distribution, and age of the infestations, 2) determine estimated rate of spread, 3) identify the locations of un-infested susceptible oaks to develop a broader tree inventory in order to estimate potential economic losses as this invasive insect continues to spread, 4) evaluate the flight periodicity, flight height, lure efficacy and mode of attack, 5) evaluate the efficacy of verbenone splat as a deterrent, and 6) provide training to a variety of audiences regarding MOB identification and management. For more information and a MOB pest alert can be found here: https://www.ucanr.edu/sites/mobpc/