One of the newest members of Lincoln’s insect family is a little wasp with a big name and no desire for human flesh.
But it can’t live without the emerald ash borer.
The Tetrastichus planipennisi is an underhanded killer, penetrating the bark of an infected ash tree with its ovipositor — the stinger on other species — to lay eggs in the larvae of the emerald ash borer.
“Then the eggs hatch,” said Dave Olson, a forest health specialist with the Nebraska Forest Service. “And they eat the ash borer from the inside-out.”
Its cousin, Oobius agrili, likes its borers even younger: It injects its own egg inside an ash borer egg, eventually hatching, growing and killing its host.
In both cases, the parasitic wasps mature — larvae, pupae, adulthood — then fly away, looking for more victims, continuing the cycle.
And the brutality of this bug-eat-bug world is now being waged in Lincoln and nearby state parks, introduced to the area by the U.S. Department of Agriculture in an attempt to slow the spread of the emerald ash borer.
The Asian beetle, about the size of a cooked grain of rice, was first confirmed in North America in the early 2000s and has been eating its way west across the U.S. since, piling up massive damage.
The insect had already killed tens of millions of ash trees — with an estimated value of $11 million — by the time it reached Nebraska, first confirmed in a Douglas County tree in 2016. It landed in Lancaster County in 2018, caught in a trap near Pioneers Park, and was discovered infesting trees in Lincoln last spring.
It’s a lethal little bug, and Lincoln’s estimated 65,000 public and private ash trees are vulnerable. The city has already started removing and replacing most of its 14,000 trees from parks, golf courses and along streets, and will attempt to prolong the lives of some with chemical treatments.
The stingless wasps were the federal government’s idea. The USDA’s Plant Protection and Quarantine program approached the state last year, and the Forest Service identified a handful of spots that could benefit from biocontrol: Pioneers Park, Mahoney and Platte River state parks and Fremont Lakes State Recreation Area.
A federal rearing lab in Michigan supplied nearly 20,000 wasps from three species and in various stages — Oobius agrili pupae, Tetrastichus planipennisi eggs, larvae and pupae, and Spathius galinae wasps.
In some cases, the lab delivers a Trojan tree limb — a branch cutting already infested with ash borer and injected with wasp larvae. Once in the field, the branch is attached to a tree that shows signs of the ash borer, and the adult wasps emerge from the cutting and start hunting in the host tree.
It’s too soon to see results, Shayne Galford, the USDA’s state plant health director for Nebraska and Kansas, said in an email. But officials will return to the release sites to introduce more wasps this year, and check for established populations in 2021. They could also add more sites, he said.
The new weapon in the war on emerald ash borers won’t stop their spread, said Olson, with the state forest service. But it could crimp it.
“It’s not going to be a silver bullet. The real goal is to get these predators set up so in a few years the emerald ash borer has additional pressure on it.”
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