About the Beetles

The Mediterranean oak borer (MOB) is an 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.

Source: Ricky Lara-Artiga, Dept. of Entomology, UC Riverside


Female beetles are light brown and 3 mm (1/8 inches) long.

MOB females can be separated from all other bark and ambrosia beetles in California by the pattern of bumps on the tip of the abdomen.

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Male beetles are smaller and rarely found outside the galleries. Males have reduced wings, cannot fly, and are not involved with the construction of new galleries.

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Mediterranean oak borers have sibling mating. Females can mate with their brothers prior to leaving the gallery and flying to a new tree to initiate construction of a new gallery where the cycle repeats. In addition, an unmated female can lay unfertilized eggs that develop into males that the female can then mate with to produce fertilized eggs. 

Beetles require 5-8 weeks to develop from egg to adult and can have two or more generations per year. In California mated females overwinter in the gallery system and emerge in late winter or spring when the temperature approaches 80° F.