Scientists fight to save iconic UC Irvine trees from invasive beetle

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If you’ve ever been to the University of California Irvine campus, you know it’s full of picturesque trees, like ficus, oak and sycamore.

However, many of these plants are under attack from an invasive beetle that's been spreading across Southern California.

"We’re very concerned," said Richard Demerjian, the school's landscape architect and Director of the Office of Environmental Planning and Sustainability.

All together there are around 30,000 to 40,000 trees on campus and Demerjian thinks this pest could wipe out hundreds and hundreds of them.

The culprit is the polyphagous shot hole borer, a beetle smaller than a sesame seed that eats its way into bark, bringing a tree-killing fungus called Fusarium euwallacea with it.

(Female polyphagous shot hole borer. Photo by Gevork Arakelian, LA County Agricultural Commissioner.)

"They actually farm that fungus as a food source," said Akif Eskalen, a plant pathologist at University of California, Riverside.

As the fungus spreads it damages the tissue trees use to move water from the roots, slowly killing it. Some plants survive years with this condition, others die after only one year.

This isn't just a college problem either.

Eskalen thinks the beetle came to California three years in some infested packing material from Southeast Asia.

The beetles can fly from plant to plant and have no natural predators here, so they were able to spread quickly through San Diego, Orange and Los Angeles Counties.

 John Kabashima, a plant expert with the UC Co-operative Extension said that there have been over 1,500 documented cases of infected trees in Orange County parks alone.

Across all of Southern California, he estimates there could be hundreds of thousands of sick trees.

(A sycamore tree riddled with holes left by the shot hole borer beetle.)

The bugs reached UC Irvine last year, when staff first noticed more than a dozen trees covered in tiny bore holes and oozing sap.

However, campus tree-lovers weren't about to lose their beloved plants without a fight.

The school made a plea to scientists across the region asking for help. Eskalen, Kabashima and others answered that call.

So far they've tried is injecting trees with a combination of pesticides and fungicides in hopes of killing both the beetle and the fungus it feeds on.

"They are going to run out of food and they are going to die," Eskalen said.

(A polyphagous shot hole borer beetle. Nearby you can see the hole that these beetles make when infesting a tree.)

John Kabashima says the team is also looking at the role irrigation plays in the spread of the shot hole borer beetle.

"For this pest the drought has probably actually helped save some trees," he said.

Kabashima thinks this might be because the fungus the beetles feed on needs moisture to grow. To test this, UC Irvine is cutting off water to one section of infested trees to see if that improves their outcome.

The team is also considering importing a different bug from Asia that kills the shot hole borer, but that would take years of study and USDA approval before it would be deemed a safe solution.

This is all complicated by the fact the beetle spreads easily and can live in dozens of different tree types.

"When we do a test on sycamores that does not necessarily translate to what’s going to happen when we treat an oak," Kabashima said.

That’s part of the reason Akif Eskalen says its unlikely researchers will ever completely wipe out this pest.

"Seems to be a little bit too late. At the end, we’re going to have to learn to live with it," he said.

Still, researchers are learning a lot about slowing the spread of the bug and treating sick trees. UC Irvine will hold a symposium later this summer to share findings with the wider community.

(Scenic Aldrich Park at the heart of UC Irvine's campus.)

For recent graduate Alison Takechi, these trees are an integral part of her college memories.

 "There’s this list called 50 things you need to do before you graduate from UCI and one of them is count all the trees in Aldrich Park," she laughed.

She's worried these beetles will put a damper on that activity, not to mention take away homes for animals and shade for students in desperate need for a quick nap in the park.

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