Though the emerald ash borer is not an immediate threat to domestic orchards or groves overseas where most olives are grown, the study yields that the killer insect finds a global commodity crop — closely related to the ash tree — an acceptable host.
“It’s a new discovery. It’s new to science. Obviously this an economically important plant,” said Don Cipollini, who headed up the research. “If (emerald ash borers) do this in nature and cause damage to these trees it would have tremendous economic impact worldwide.”
Cipollini, a biology professor, is careful to not overstate the alarm to olive growers, but the ash borer is now found to have naturally infested another ash relative, the white fringetree, an ornamental that grows in Ohio and elsewhere. That revelation came as a surprise when Cipollini made that discovery in 2014, he said.
Work on the white fringetree led Cipollini, also the director of the Environmental Sciences Ph.D Program, to wonder what other plants might be friendly to the beetle.
Credit: Chris Stewart
Credit: Chris Stewart
As devastating as the beetle has been to ash trees, those trees don’t have a direct connection to food. An olive tree infestation — which would undoubtedly raise the price of both olives and olive oil — would be another matter entirely.
Olive growers don’t need another pest, said Adin Hester, president and CEO of the Olive Growers Council of California
Devastating pest
The emerald ash borer has been in the U.S. at least since 2002. The most devastating pest to ever hit American forests is believed to have arrived from Asia in shipping material.
The infestation has now widened to 30 states. Emerald ash borer was first discovered in Michigan in 2002 and detected in Ohio in 2003; the most recent state reached is Delaware, where it was found in August. It has already killed hundreds of millions of ash trees in North America.
The cost to communities is staggering. Damages in just four Midwestern states including Ohio are estimated at between $13.4 billion and $26 billion, according to a U.S. Forest Service Northern Research Station report.
The local impact has been huge as well. Before the beetle’s invasion, cover mapping showed ash trees made up 21 percent of Five Rivers MetroParks’ forested areas, said Mary Klunk, regional parks and conservation manager.
Klunk estimates 80-90 percent of ash trees in the Miami Valley have already been affected or will be. The park district has removed 3,200 ash trees since 2011 in high-use areas where a dead tree presents a danger to people.
“Trees in natural areas are left where they fall,” Klunk said.
‘Aha’ moment
Beginning in the spring of 2015, WSU’s Cipollini and then-doctoral candidate Chad Rigsby of Springfield inoculated small olive stems with emerald ash borer eggs. They documented what happened within the bark of the trees kept in a greenhouse connected to Fawcett Hall.
After three weeks they had an answer: The eggs developed within the olive test stems.
“That was one of our first ‘aha’ moments.” Cipollini said. “Live larvae actively feeding on these trees. That was like, ‘wow, oh no.’”
That led to subsequent studies this year on bigger trees and larger, commercially cultivated stems from a common Spanish variety in California called Manzanilla.
Debarked stems revealed numerous larvae-feeding galleries.
Emerald ash borer larvae grow to between 1 and 1½ inches while devouring the phloem, or the tissue within the bark that moves water, sugars and carbohydrates between the tree’s canopy and its roots. A tree succumbs after larvae “girdles” its trunk or branches, eating away enough of the important circulatory tissue.
The researchers exposed other stems to an artificial winter by using incubator to trick the larvae into pupation, or transformation.
On Aug. 31 an excited Donnie Peterson called Cipollini at home. The doctoral student from Black River Falls, Wis. noticed movement in one of the stems. He rushed the stem to Cipollini’s house so they could roll a camera as an adult emerald ash borer chewed its way out of the bark.
“That is indeed the first emerald ash borer that we’ve ever seen come out of an olive tree,” Cipollini said. “Nobody else in the world has something like that.”
Dealing with ‘nasty creature’
Olive growers in California already have their hands full with an invader: the olive fruit fly, said Hester.
Sometime prior to 1998, a shipment of olives infested with the fruit fly made its way from Baja Peninsula to northern California, leaving behind a load of trouble of California’s olive growers.
“Within the first three or four years, every county in California that grows olives had been infested with fruit flies,” Hester said. “It’s a nasty little creature.”
The fly larvae worm their way through the fruit, making table olives not only unappealing but worthless, he said.
In the Mediterranean, fruit fly blight and “olive tree leprosy” sent 2014 production down 35 percent in Italy — the second largest producer after Spain. A drought that same summer in Spain caused a disastrous harvest there. Due to the shortage from the two countries that together produce 70 percent of the world’s olives, Europeans paid on average 19.8 percent more for olive oil during much of 2015, according to analysts. Prices are still volatile now that the “leprosy,” Xylella fastidiosa, is wreaking havoc in Spain.
Cipollini said the emerald ash borer is not yet near the Mediterranean olive-growing regions, but has been documented in Russia near Moscow.
No other state comes close to California in domestic olive production. At peak, about 38,000 acres were devoted to table olive production, but that is on the decline, Hester said. About 30,000 acres – and growing – support olive oil makers. But even California pales next to Spain, which leads world production and supplies about 45 percent of the world’s olive oil. Olives are also cultivated in Australia and parts of South America. In the U.S., limited production occurs in Arizona, Florida, Georgia, New Mexico, Oregon, and Texas.
Olive cultivation is undergoing a revival in the South, said Vicki Hughes, executive director of the Georgia Olive Growers Association. Olives were brought to Georgia by the Spanish in the 1700s but disappeared by the next century.
In 2009, growers in Georgia started high-density planting of olive trees, which now produce on a modest 650 acres.
“Next year we are expecting to see a very rapid growth in acreage,” she said.
‘It’s a matter of time’
The widening map of emerald ash borer infestation is a concern both for olive growers in the South and California.
United States Department of Agriculture maps show the beetle’s range has expanded so far south that it is now only a couple of counties away from olives are able to grow, roughly below Macon. And the emerald ash borer has found its way near Denver, where the Continental Divide and two other states separate the beetle’s westernmost incursion from California olive groves.
“That’s a good question whether it can make that big jump from the Rocky Mountains into California, Hester said. “But you know anything is possible.”
As proven with both the olive fruit fly and the emerald ash borer, invasive species often take big leaps.
“There’s no reason to believe those kinds of jumps won’t happen again,” Cipollini said. “Plus there are contiguous populations of individual ash trees planted in towns and cities and growing all the way out to California.”
Cipollini said susceptible ash trees grow right up to and intermingle with olive trees in California and Oregon.
“The emerald ash borer will get to California,” Cipollini said. “It’s a matter of time.”
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