No sign of tree-killing invasive beetle in Sacramento County after first months of surveillance

An invasive beetle that has unleashed catastrophic damage on trees in Southern California has not been found in Sacramento County after the first few months of a statewide surveillance program designed to monitor its movements.

Known as the shot hole borer, the invasive bug is being closely watched through a partnership between counties and UC ANR researchers in the integrated pest management program. Sacramento County officials deployed several traps near riversides in April, and so far there’s been no sign of the bug, said county Agriculture Commissioner Chris Flores.

“The good news is we have not found anything,” Flores said. “We’ve had traps out since April and we have not found anything yet.”

Flores said the traps were placed in 17 locations along rivers and left out for about one month. The devices are supposed to attract the beetles, which can fly, to a sticky panel with pheromones. They were placed in riparian areas as well as in green waste facilities and firewood lots. Flores said the traps will go out again once the temperature drops and the beetles get into their flight patterns.

The University of California will reimburse the county for as much as $21,500 of the costs to continue surveying for the bug until next year. The program is a part of a $5 million appropriation from the legislature for “stakeholders to develop a plan for the cure or suppression of diseases associated with the spread of invasive shot hole borers.”

Since the first shot hole borer was found in 2003, the critter has infested thousands of trees in Southern California and the Central Coast. Native to southeast Asia, the beetle burrows into trees and releases spores to create a fungus that it eats exclusively. The fungus restricts the trees’ water distribution and slowly kills it over time.

The shot hole borer can survive in at least 64 different types of trees, including avocado and almond trees.

But it prefers trees that grow near riversides like willows, cottonwoods and sycamores. Its resilience has made it a key concern for urban foresters, including in the city of Sacramento.

Spreading throughout Southern California

Two types of the shot hole borer are present in California: the polyphagous, which loosely translates to excessive desire to eat, and kuroshio. The kuroshio shot hole borer is well-established in San Diego County and currently also is present in Orange and Santa Barbara Counties. A single beetle was caught in a trap in San Luis Obispo County in 2016.

The polyphagous shot hole borer is now present in Los Angeles, Orange and Riverside counties and has also spread to San Bernardino, Ventura and Santa Barbara counties. A single beetle was caught in a trap in Santa Cruz County in 2014.

For now, the trail of the beetle stops there, said Randall Oliver, a UC ANR spokesman for the integrated pest management program.

“The various trapping programs with most of the counties throughout most of the state are fairly new so there’s not a lot of data that’s available yet,” Oliver said. “We’re trapping statewide both to confirm the spread of the beetles but also to, where possible, do a negative confirmation that the beetles are not in these other locations.”

This story was originally published July 22, 2021 at 5:00 AM with the headline "No sign of tree-killing invasive beetle in Sacramento County after first months of surveillance."