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Tiny insect menace chokes trees across Cape Cod

October 20, 2013

DENNIS, Mass. (AP) — A minuscule menace is buried in the gnarled, deformed limbs of black oak trees across Cape Cod, slowly choking them to death.

Its common name — the crypt gall wasp — is like something out of a horror movie, but for property owners, the evil it wreaks is all too real.

Hordes of the tiny wasps deposit their eggs in the trees’ new spring growth. The larvae grow inside the wood and form swelled chambers known as galls.

A year later, the adult wasps — measuring only 5 millimeters — emerge through pinprick holes in the wood and repeat the cycle over again, cutting off the system that distributes nutrients throughout the tree.

Starved of food, twig growth slows, leaves turn brown and eventually, if the infestation continues unabated, the tree may die.

Even though much is known about the tree-killing culprit, much is still a mystery, including whether it is a native or wash-ashore.

“So little is known about the life cycle,” Russ Norton, educator in horticulture at the Cape Cod Cooperative Extension, said.

Norton, who is monitoring a research site in Nickerson State Park in Brewster, and other researchers are working to fill in those gaps.

Recently, workers with Arborjet, a Woburn company that tests and sells tree injection systems and insecticides, took a stand against the crypt gall wasp in Dennis Village Cemetery, a setting seemingly made for the fight against the pernicious pest with the deathly name.

Arborjet is working with University of Massachusetts-Amherst professor of entomology Joseph Elkinton and one of his graduate students to study the best ways to deliver insecticide that will stop the wasps in their tracks.

Researchers are not even convinced the species has been correctly identified, Elkinton and Arborjet officials said.

“We’re starting from square one with this insect,” Elkinton said.

Widespread damage from the wasp became apparent on Martha’s Vineyard a couple of years ago, he said.

But, while a similar infestation on Long Island crashed after only three years, the outbreak on the Vineyard has lasted longer.

On Cape Cod, property owners and arborists started seeing widespread damage in 2012.

“You probably don’t even see the symptoms for two years,” Peter Wild, CEO and founder of Arborjet, said.

At the Dennis Village Cemetery, Arborjet’s Don Grosman demonstrated how the injection systems use the tree’s vascular system to transport chemicals to fight the wasps, Grosman said.

A small black plug called an arborplug is inserted into holes drilled into the trunk, he said.

A needle attached to a pressurized reservoir is then connected to the plug, forcing the chemicals into the tree’s active tissue.

The company is testing two solutions: TREE-age, which relies on emamectin benzoate, a pesticide that causes insect paralysis, and IMA-jet, based on imidacloprid, a pesticide derived from synthetic nicotine, according to the National Pesticide Information Center, a collaboration of the University of Oregon and the U.S. Environmental Protection Agency.

Unlike spraying or other methods, injecting the chemicals keeps them contained within the tree and out of the surrounding environment, Grosman said.

“We pride ourself in that we put everything into the tree,” he said.

Even so, only a small amount of each product is required, he said.

For a tree with a 20-inch diameter, only 8 grams of the solution is used, Grosman said.

Although work in Hawaii on a similar infestation in banyan trees has shown that the method works, the exact effects on the crypt gall wasps are not yet clear, Grosman said.

About 50 trees in Barnstable, West Harwich and Dennis were injected with the two chemicals. An additional 20 trees are being monitored as controls.

The effect on different levels of infestation is being studied, Grosman said.

The trees will be checked over several years to see how long the chemicals keep the wasps at bay.

So far, there are pockets of the infestation in black oaks across the Cape, he said.

“It’s widespread but at the same time it’s somewhat sporadic,” he said.

The reasons for one tree succumbing to the wasp and another tree remaining healthy aren’t clear, Grosman said.

Generally trees become susceptible to infestation when they are stressed.

This could be because of changes in the weather such as drought or it could be because of other factors, such as disease or the amount of salt used on nearby roadways, Grosman said.

At the cemetery, digging for graves could even be a factor, he said.

Natural conditions could lead to a collapse in the wasp population, such as what happened in Long Island, he said.

Infestations of exotic species are the cost of climate change and global trade, Wild said.

Still, like so much else with the crypt gall wasp, there is much more to be learned, both men said.

Education is the first step, Wild said. “Usually by the time you call the arborist, it’s time to cut the tree down,” he said.

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