An oak tree in Henry Coe State Park. (Nik Altenberg — Santa Cruz Local file)

SANTA CRUZ COUNTY >> Two meetings are planned this week to share information about an invasive beetle that threatens an unknown number of trees in Santa Cruz County.

An infestation of the invasive beetles was first detected along Zayante Creek near Felton in 2024. Called shothole borer beetles, the tiny insects hail from Southeast Asia and are problematic locally because they bore into trees and bring a deadly fungus with them which can cause tree dieback. The female beetles, generally a bit larger than males, are about 3.78 mm long or roughly 5/32 of an inch.

The beetles are known to affect trees across urban, rural and agricultural areas. In Santa Cruz County, box elders have suffered the most destruction but the beetles have also been found in California sycamore, coast live oak, willow and black cottonwood trees.

The County of Santa Cruz and UC Cooperative Extension are planning two meetings this week to inform residents about the issue, how to identify an infestation and how the community can help tackle the problem.

Signs of an infestation may include “small, round entry holes, wet staining, gumming, boring dust or sugary buildup on trees,” according to a county press release. Dieback from the fungus could cause “pale and wilted leaves and branch dieback,” according to the UC Agriculture and Natural Resources website.

If an infestation is suspected, residents are asked to call the county Department of Agriculture at (831) 763-8080. A shothole borer detection assessment and more information about the insects are available on the website. 

The species found in Santa Cruz County was the first instance of the greater shothole borer detected on the West Coast. Related species of shothole borers were first identified in Southern California in 2012 in a backyard avocado tree and have since caused the loss of tens of thousands of trees.

U.S. Forest Service researchers estimated in a 2017 study that 27 million urban trees in and around Los Angeles County could ultimately be lost to the beetle. The extent of the threat to trees in Santa Cruz County is unclear.

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