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Serving the Entire Sacramento Area, Including Fair Oaks & Folsom
North Area: 916-925-0328
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Serving the Entire Sacramento Area Including Fair Oaks & Folsom
North Area: 916-925-0328
South Area: 916-991-1551

A Short Guide to Invasive Shot Borer Beetles in California

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Borer Beetle
People once saw two invasive species of ambrosia beetles - of which there are 3,500 species - as no more than a nuisance. Today, biologists and foresters throughout California are worried that the two beetle species will destroy entire stands of trees in the state. Here's what you should know about these beetle species and your trees.

Invasive Shot-Hole Borers Include Two Species

That a beetle no bigger than a sesame seed can take down a towering oak might be hard to believe. But two species of invasive borer beetles may be responsible for the death of up to one-third of California's urban tree canopy.

People once thought the Polyphagous and Kuroshio shot-hole borers to be the same invasive Asian species. Today, biologists recognize them as two distinct species. However, biologists consider the two borer beetles alike enough to both label them as invasive shot-hole borers. Here are the few differences between the two. 

Polyphagous Shot Hole Borer (PSHB)

This beetle is native to Vietnam and invades hundreds of tree species by tunneling inside and creating galleries for eggs. The beetles spread fungi, including Fusarium euwallaceae sp. and Graphium sp., along the galleries. Hatching larvae eat the fungi and exit the tree trunk to infest other trees.

The PSHB needs certain tree hosts to successfully lay eggs, although it will infest other trees, too. The beetles choose live trees over dead or dying trees because the fungi they spread need water to grow.

Trees that can host the PSHB eggs include:
  • Avocado
  • Box elder
  • California sycamore
  • London plane
  • Coast live oak
  • Japanese maple
  • Red willow
The PSHB spread the fungi and cause at least 110 species of trees to die as the tree can no longer take up water and nutrients. After the tree dies, the beetles move on to new, healthy trees.

Kuroshio Shot Hole Borer (KSHB)

This Taiwanese native beetle invades and infests trees with the same strategies used by the PSHB, although the fungi they carry are slightly different. The KSHB is not as widespread in California as the PSHB, but large populations are found along southern coastal areas. Damage from the KSHB includes the death of 180,000 willows in the Tijuana River Valley.

PSHB and KSHB look exactly alike, with females being no longer than 0.1-inch long and males half that size. The beetles are dark brown or black. Because they have no known predators in California, both invasive shot borer beetles have expanded unchecked throughout the state.

Chemical Treatment for Shot Hole Borers Doesn't Exist

Arborists, foresters, and researchers have tried many methods to eradicate the PSHB and KSHB and treat affected trees. No chemical treatments have proven successful.

A PSHB or KSHB infestation does not kill every tree. Some tree species are able to hold off the infections. PSHB and KSHB infestations are notable for the tiny holes that the beetles drill into tree trunks. Pine trees can close the holes with resin, while cherry trees excrete a juice that turns hard to plug the beetle holes.

Other trees including sycamores, box elders, and oaks will die rather quickly once bugs infest the beetles. The only thing you can do is remove the trees and plant new trees to replace those you've lost. Hire a tree service to handle this work, since the dead wood from the tree can spread the borer beetles to other trees.

Don't use any of the wood from an infected tree for firewood on camping trips or for mulch around your property. Let the tree service haul the wood off your property.

You can kill up to 98 percent of the beetles by grinding up the infected wood and covering it with material that heats up the pile under sunlight. Researchers are also investigating bacterial and biological controls for the beetles.

Contact AAA Tree Service today to schedule an inspection of your trees. Many types of boring beetles infest trees in the Sacramento region, and some can be controlled with proper treatments. We also safely remove infested trees throughout the Citrus Heights, Elk Grove, Fair Oaks, Folsom, Orangevale, Rancho Cordova, Roseville, and West Sacramento areas.