Twolined chestnut borer (Agrilus bilineatus) is a native beetle that attacks weakened oaks of every species in Minnesota. It lives in and feeds on the inner bark and cambium, a layer of cells between the bark and the wood. When trees are not stressed, twolined chestnut borer confines its attack to unhealthy trees or broken branches. Oaks become susceptible to attack when tree vigor is reduced from drought, construction, defoliation, or disease. Infested oaks usually die after 2-3 years of infestation.
The drought in 2012 caused widespread outbreaks of twolined chestnut borer, resulting in the death of thousands of oaks in central and northwestern Minnesota from 2015 to 2018.
Other oak problems can easily be confused with twolined chestnut borer, and the presence of twolined chestnut borer doesn't necessarily mean it is the primary problem. Read about diagnosis in the Identification section.