Non-Native Insect That Kills Trees Detected in San José

SAN JOSE, CALIF. — The County of Santa Clara Division of Agriculture announced Friday, Aug. 23, that the invasive shothole borer, a non-native beetle that attacks more than 65 species of tree in California, has been detected in San José.

It’s not clear when the beetle got here or how widespread the infestation is – it’s possible the insects have been in San José for several years. Researchers are conducting surveillance to determine the extent of the infestation.

The invasive shothole borer is tiny – females are about the size of a sesame seed, and males are smaller. The insect tunnels into host trees, introducing a fungus that serves as food for the beetles and their larvae. The fungus causes a disease in trees that prevents them transporting water and nutrients, damaging and sometimes killing them.

It is likely too late to eradicate the invasive shothole borer from San José, but there are effective ways to manage the threat posed by the insect. The most important step right now is to conduct a thorough visual survey of the San José area to identify infested trees.

“We’re asking for the community’s help in identifying trees that have been attacked by invasive shothole borers, which will help us determine the extent of the infestation,” said Drew Raymond, acting agricultural commissioner for the County of Santa Clara. “While we probably can’t get rid of the invasive shothole borer at this point, we can contain the infestation to protect as many of our trees as possible.”

The Division of Agriculture asks residents and property owners to be on the lookout for signs of invasive shothole borer infestations.

The easiest way to identify an infested tree is an entry or exit hole that is perfectly round and roughly the size of the tip of a ballpoint pen. Other signs include wet staining, gumming, frass (insect waste), boring dust, and sugary buildup around entry and exit holes.

If you see any of these signs on trees on your property, contact the Division of Agriculture at [email protected] or (408) 918-4610. Division biologists can help you confirm whether the invasive insect is present.

Residents who need help removing infested trees or disposing of infested wood should contact a professional arborist. Do not move or throw away infested branches or logs unless you have taken proper steps to sanitize the wood in consultation with an arborist.  

Researchers have confirmed that the non-native pest is capable of killing 17 species of tree, including the box elder, California sycamore, valley oak, Japanese maple and American sweet gum. Dozens of other tree and shrub species are known to host the invasive beetle, such as the California buckeye, coast live oak, avocado and acacia.

Researchers don’t know how the invasive shothole borer, which is not a strong flyer, arrived in the South Bay. It may have been due to the movement of infested green waste or firewood. Other ways the beetles travel from one place to another include nursery stock and packing materials such as wood pallets or crates.

The beetle was discovered in Southern California in the early 2000s and has killed tens of thousands of trees in seven counties: Los Angeles, Orange, Riverside, San Bernardino, San Diego, Santa Barbara and Ventura.

For more information on the invasive shothole borer, you can read a thorough overview produced by the Statewide Integrated Pest Management Program.

Photos of the invasive shothole borer are available at this WeTransfer link.

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