Mother Nature cutting moths down to size
Leafy trees should make a comeback with gypsy moths on the decline
WOONSOCKET – After two summers of widespread defoliation of trees by leaf-eating gypsy moth caterpillars, this may be the season when northern Rhode Islanders finally see some relief, state forestry officials say.
State Forest Health Program Coordinator Paul Ricard says he’s cautiously optimistic that natural caterpillar-killing pathogens have been present in the ecosystem in sufficient concentrations to prevent the sort of intensely widespread infestations that defoliated hundreds of thousands of acres of woodland in the state during the previous two years.
“It looks like all the conditions are there to knock down whatever type of an infestation that starts,” said Ricard. “What I am telling people is there may be some locally intense infestations but it won’t be nearly as widespread as it was the last two years.”
Ricard’s assessment is based on the number of egg masses he’s located at 142 wooded observation plots scattered roughly evenly about the state. He’s found “a little over a thousand” egg masses in total, throughout the state. Each egg mass is capable of producing anywhere from 200 to 600 gypsy moth caterpillars.
“Last year there were tens of thousands of egg masses,” said Ricard, who is headquartered at the George Washington Management Area in Glocester. “It is promising but before this whole infestation started I would be
lucky if I could find 20 egg masses throughout the state. Comparatively speaking, it is a tremendous improvement, but there is still that potential to see some level of infestation.”
The heaviest concentrations of egg masses he’s seen are in parts of Smithfield and North Smithfield, said Ricard.
Gypsy moths should be morphing from eggs to tiny wormlets, about a quarter-inch long, any day now, if they haven’t begun to do so already. Depending on the temperature, the tiny caterpillars emerge between the second and third week of May, but property owners may not notice them until they start eating foliage, leaving tiny, pellet-size holes in leaves.
“Typically, gypsy moths are out by the second week of May,” said Ricard. “They were easily seen when there were so many in the environment. They’re not going to be so readily visible this year. When they’re going to be visible is when there are signs of feeding. Beginning this week and into the following weekend is when people will begin to see small shotgun-type holes in their leaves and they’re going to see the caterpillars growing.”
Egg masses look like quarter-sized, sand-colored patches of fuzz that are typically found on tree trunks, the underside of limbs and beneath the eaves of sheds and garages. They are deposited there in the late summer and early fall by adult gypsy moths after the insects transform from their caterpillar, or larval phase, into the winged creatures.
In the worst gypsy moth invasion the state had seen since the 1980s, the crawly pests defoliated 226,000 of the state’s roughly 450,000 acres of forest woodland in 2016, much of it in the central and western part of the state, according to Ricard. The following year, the devastation was even worse – the bugs decimated 313,000 acres of woodland.
But the conditions that gave rise to the critter population bomb began much earlier, according to the state forester, who says Mother Nature laid the foundation with drought in 2013. The parched ecosystem inhibited the spread of two key pathogens that are deadly to gypsy moths – one a fungus called entomophaga maimaiga, the other a virus called NPV, or nuclear polyhedrosis virus.
Last season’s rainy spring bumped up the concentration of those pathogens to a point that was sufficient to sicken many caterpillars before they got the chance to pupate into moths, mate and lay eggs. Similarly, this spring, said Ricard, it appears to have rained enough at the right time to keep enough of the pathogens in the atmosphere to tamp down the next wave of caterpillars.
“Even though egg masses are way down there were still a significant number out there,” he said. “The potential is there for some level of an infestation. That being said, at the end of last year we saw a massive die-off of caterpillars from both entomophaga fungus and NPV. Based on the fact that there was a lot of virus and fungus in the environment already and that we have so far had sufficient rainfall at the right time to allow the fungus to germinate, it looks like all the conditions are there to knock down whatever type of infestation that starts.”
Gypsy moth caterpillars gravitate toward oak and other hardwoods as their primary food source, but they’ll try almost anything if they exhaust their favorites, even conifers, said Ricard.
After two successive seasons of widespread defoliation, some property owners may be noticing trees that aren’t leafing out this spring. Ricard’s advice: Keep your fingers crossed – they might not be dead.
The back-to-back defoliations have been extremely stressful for trees, said Ricard, and even some that leafed out with smaller, stunted growth late last summer, after the defoliation, might be having a bit of trouble getting their springtime act together.
“Those trees could be alive,” said Ricard. “They could be late bloomers. Occasionally trees will go dormant for a year and then come back the following year. Or there could be a leaf-out later this year with smaller than usual leaves.”
An exceptionally cold spring may be also be contributing to the slower-than-usual leaf-out for some trees.
“Spring got a late start,” he said. “All of a sudden it was here. Trees are a little slow to react to that.”
There are few effective strategies for curbing an infestation as intense as those of the previous two years, especially for homeowners who live in densely foliated, rural areas. Gypsy moths can sail for miles in the breeze, dangling from fine strands of silk-like thread that they create. So even vegetation that’s been treated with a caterpillar-killing spray – several varieties are available at hardware stores and garden centers – is susceptible to an onslaught of new gypsy moths riding in on the wind.
“That’s why the state doesn’t spray for gypsy moths,” said Ricard. “It’s expensive, and it’s not effective.”
But Ricard said a homeowner who wants to protect one or two cherished ornamentals can use products containing a natural bacteria known as bacillus thuringiensis, often abbreviated as Bt, or its relative, bacillus thuringiensis kurstaki, or Btk. One of the more popular brands is Thuricide, which works well on a many varieties of wormy varmints that feed on plants, including forest tent caterpil- lars and eastern tent caterpillars.