Cold spell may slow beetle’s march

Recent cold weather cold help slow the spread of emerald ash borers. -RA ARCHIVE

Recent cold weather cold help slow the spread of emerald ash borers. -RA ARCHIVE

There may be a silver lining to the polar vortex.

The tree-killing emerald ash border, which has been chewing its way through ash trees in four Connecticut counties, suffers in the bone-chilling cold.

In St. Paul, Minn., the U.S. Forest Service has learned that borers are succumbing to below zero temperatures.

It’s good news at the Connecticut Agricultural Experiment, where entomologist Dr. Kirby Stafford said the cold likely accomplished a partial kill off. Just how many of the invasive pests survived won’t be known until later this year.

For instance, Stafford said, it’s unclear whether the beetle larvae is able to accommodate a certain amount of cold weather insulated beneath tree bark. Ticks, he noted, also succumb in deep cold but are able to secret themselves in protective leaf litter.

Temperatures in Connecticut earlier this month reached minus 11 in Norfolk, with unconfirmed colder readings in the area, according to the U.S. Weather Observatory Station in Norfolk. Below zero readings were recorded across the state.

According to the Forest Survey study, 98 percent of the beetles succumbed at minus 30. At minus 20, 79 percent died and at minus 10, 34 percent died. There is also some mortality at below zero temperatures, Stafford said.

“It’s unclear whether our temperatures were low enough, how long the exposure has to be and whether there was any adaptation,” Stafford said. “We’ll see some mortality at least.”

Any delay in the beetle’s advancement could buy time for state and local governments to slow the steady march.

The borer is held responsible for the death of tens of millions of ash trees in 20 states since it was first identified in Michigan in 2002. Ash trees make up between 4 percent and 15 percent of Connecticut’s forests. The beetle has been found in 15 towns and four counties in Connecticut, including Beacon Falls, Prospect and Naugatuck.

Biosurveillance to track the borer’s movements will continue this summer, Stafford said.

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