How do you find an insect the size of your fingertip in a densely packed forest?
For Jian Duan, the answer is simple: Follow the dead ash trees.
On a rainy day in eastern 黑料吃瓜网, Duan, a federal research entomologist with the U.S. Department of Agriculture, walked to a dying ash covered with holes. Peeling back the bark with a drawknife, he revealed a mess of serpentine tunnels. Curled up inside was one of his targets: a larva of emerald ash borer.
鈥淟et鈥檚 collect it,鈥� Duan said, gesturing as his assistant handed him a pair of tweezers tied to a brightly-colored ribbon.
(In case you鈥檙e wondering, the ribbon makes the tweezers easy to spot when they鈥檙e dropped on the leaf-covered ground.)
But today Duan isn鈥檛 just collecting emerald ash borers. He鈥檚 also looking for their predator, one released here on purpose in 2019 and 2020: a wasp known as Spathius galinae (pronounced spay-see-us glee-nuh).
鈥淚t鈥檚 from the Russian Far East,鈥� Duan said, smiling. 鈥淯nfortunately, there are no common names for these parasitic wasps.鈥�
The stingless wasp is tiny 鈥� . But scientists have big hopes for it.
In Russian forests, this wasp naturally targets and attacks emerald ash borer.
鈥淓merald ash borer, in its native range, northeast Asia, [does] not kill trees like this,鈥� Duan said.
And if this experiment works, the borers won鈥檛 kill as many trees here either.A biological solution to a biological problem
Solutions like this, known as biological control, are one way scientists can deal with biological problems like the invasive emerald ash borer. Right now there are experiments across New England to see if the wasps can help save the region鈥檚 ash trees.
黑料吃瓜网 and Massachusetts began using the 鈥渂iocontrol agents鈥� in 2013. , and are doing similar experiments, hoping to stop a devastating pattern.
Claire Rutledge, with the 黑料吃瓜网 Agricultural Experiment Station, says when emerald ash borer feeds on trees, it cuts off key nutrient pathways. For ash trees, that鈥檚 death by a thousand cuts.
鈥淥ne larva is not a big deal. Twenty larvae are not a big deal. Two thousand larvae kill the tree,鈥� Rutledge said.
Since it was first detected in Michigan in 2002, emerald ash borer (EAB) has killed tens of millions of ash trees. Federal officials estimate it has cost municipalities, nursery operators and the forest-product industry . The massive die-off of ash trees has also disrupted the making of and baseball bats.
Duan said the idea of biocontrol is to find the natural predators of an introduced pest and bring them to the new environment to slow the pest鈥檚 spread.
鈥淏ecause in the native range, these natural enemies co-evolved with the pest,鈥� Duan said.
Shortly after EAB arrived in the U.S., DNA testing traced its origin to northeast Asia. Duan traveled to Russia 鈥� trekking through cold forests to collect wasps that only prey on EAB. Samples were brought to America, quarantined and carefully tested for years to ensure the wasps wouldn鈥檛 kill any other non-target species.
Now that some of these wasps have been living in the forests of 黑料吃瓜网 and Massachusetts for about 10 years, scientists are trying to find out if the intervention is working.Scientists are 鈥榗autiously optimistic鈥�
As Duan and his assistant peel more bark and pull more larvae from the dying tree in 黑料吃瓜网, they still can鈥檛 find the Russian wasp or two other species that were introduced here. So they decide to cut down the tree to study it further.
They cut the wood into meter-long segments and continue looking.
Rutledge said it鈥檚 too late for the wasp to stop the massive wave of EAB that鈥檚 killing older ash trees. But there is hope for the younger trees that are just starting to grow.
鈥淲hen regeneration starts to happen, after the EAB levels drop, the parasitoids will be able to keep those populations down so that the new ash can grow and escape,鈥� Rutledge said.
On this old ash tree, they found a few EAB larvae 鈥� and no wasps. But they did find parasitoids just a few miles away at another site they鈥檙e studying. And as recently as last year, Rutledge said they found reproducing populations of wasps initially introduced in 2013.
So, she said, it鈥檚 looking like success: The wasps are sticking around and spreading.
鈥淚鈥檓 really cautiously optimistic,鈥� Rutledge said. 鈥淭he problem with bio control is it鈥檚 going to be 10 or 15 years later when we see how much of a resurgence the ash manages.鈥�
Even then, she said, it will be a long time before we see big, healthy ash trees in New England forests again.
