Trees may get a break from very hungry caterpillars
Spring rains fell. The fungus flourished. The virus quickened.
Now, dead spongy moth caterpillars are rotting in much of the state's Northwest Corner.
The joint plagues — fungus and virus combined — didn't come soon enough to stop the defoliation of tens of thousands of acres of trees this year. The spongy moth — formerly gypsy moth — infestation may match last year's total of 45,000 acres of denuded forests.
But next year, Litchfield County's humans may be spared the eerie sight of a bare winter treescape in late spring. The trees — stressed out after having lost leaves in two successive years — may get a needed return to normal growing.
“Thank goodness,” said Chris Martin, head of the state Department on Energy and Environmental Protection's forestry division.
“It's not going to have much effect this year, but it will reduce the infestation next year,” said Victoria Smith, deputy state entomologist at the Connecticut Agricultural Experiment Station in New Haven.
It's hard to tell what damage the infestation brought to Litchfield County's forests.
It affected a core of towns — Sharon, Cornwall, Falls Village, Warren, — in 2021 and returned this year. It spread to some adjoining towns and across the border into New York.
“I believe it was all over Warren this year,” said the town's first selectman, Gregory La Cava.
Kent First Selectman Jean Speck said her town's trees were eaten by the caterpillars this year.
“Oh, my goodness gracious, yes,” Speck said. “It's had a huge impact on the town. You drive up along Route 7, the defoliation makes it look like a war. We have a 100-year old apple tree in our yard that lost all its leaves.”
However, towns to the south and east have been spared.
“We haven't seen any,” said New Milford Mayor Pete Bass. “We'll keep our fingers crossed.”
Smith, of the agricultural experiment station, said healthy trees can recover from two or three years of defoliation, by growing new leaves.
But DEEP's Martin said if a tree is old or if it's stressed by other things — like disease or drought — it may not recover.
That's what happened in eastern Connecticut from 2016 to 2018 when spongy moth outbreaks combined with a multi-year drought. The infestation spread to 287,000 acres of forest, and killed tens of thousands of trees there.
Spongy moths — Lymantria dispar — are a nonnative invasive pest.
An enterprising New
Englander, Leopold Trouvelot brought the moths to his home in Medford, Mass., in 1866, hoping to start an American silk industry. The industry never happened, but the moths escaped in 1869 and began reproducing in the greater world.
The mess of munching caterpillars, hanging by strands and dropping poop as they eat their way across the landscape, spread quickly, causing devastating outbreaks throughout the eastern U.S.
In 1910 and 1911, and again in the 1980s, people tried a biocontrol to combat the spongy moth caterpillars by releasing a Japanese, caterpillar-eating fungus, Entomophaga maimaiga.
It had no effect. But then, miraculously, it blossomed forth in southwestern Connecticut in 1987 and began wiping out spongy moth caterpillars like a fungal Grim Reaper.
“I was working down there at the time,” DEEP's Martin said. “All the caterpillars were dying and we were asking ‘What's going on?' ”
What entomologists have learned since is for the fungus to function, we need a fairly wet spring to release the spores. That happened this year.
A virus kills the spongy moth caterpillars — nucleopolyhedrosis virus or NPV. It exists naturally in low levels in spongy moth caterpillars. During big infestation, when the caterpillars are stressed by the competition for food, it can kill them.
That's what happened this year in Litchfield County.
The caterpillars hatched from last year's egg mass and began chomping.
But a wet-enough spring enlivened the fungus. The size of the infestation let the NPV virus do its work, as well.
Martin said you can tell which agent of death is working by the posture of the corpse. Caterpillars killed by the virus bend into a V-shape. (V for virus? V for victory?) Those killed by the fungus stretch out in a straight line.
With any luck, next year they'll be gone and June's greenery will be lush and undigested.
“It's a testament to the resiliency of our forests,” Martin said. “They've been hammered. But they come back.”