MAKE WAY FOR MOTHS
Tree-killing gypsy moth infestation could be even worse this year, forester says
GLOCESTER — If you thought the gypsy moth invasion was bad last year, it’s quite possible you ain’t seen nothing yet.
State Forester Paul Ricard told a gathering at the Manton Free Public Library several days ago that the infestation of 2017 could be the worst in the state since the early 1980s, causing widespread defoliation.
There are a few environmental variables that could still affect the scale of the onslaught. But Ricard said the dire forecast is based on the annual count of gypsy moth eggs masses on the trunks of trees in 142 test plots distributed evenly through the state. The egg masses appear as fuzzy, brownish patches on the trunks of trees, where they are deposited in the fall by adult moths.
Last spring, some 226,765 acres of woodland were defoliated across a large swath of the state. That damage came after foresters counted about 3,500 egg masses on its 1,000-squarefoot test plots.
The egg count from the test plots last fall – the numbers that will most likely drive the gypsy moth population this season – is far higher than it was in the fall of 2015. Foresters counted 35,000 egg masses – a tenfold increase – on test plot trees in 2016. Those numbers could yield a population of 1.3 trillion caterpillars in roughly 400,000 forested acres across the state.
“That’s what’s out there,” Ricard said. “We might be in for a bad year this year.”
A Glocester resident who is stationed at George Washington Management area, Ricard was invited to speak by the Glocester Democratic Town Committee. About 70 people attended, many of them gasping in horror as Ricard explained the potential
scope of the coming infestation.
“Why isn’t the state spraying?” someone asked.
Citing scant resources and the concerns about the harmful effects of spraying on beneficial insects, Ricard explained that DEM has no plans of mounting an aerial attack on gypsy moths this season.
Generally, gypsy moths begin hatching as tiny wormlets in mid- to late April to begin feasting on tree foliage and growing until mid- to late June, at which point they enter the pupation phase of their life cycle. That’s when they form a cocoon, or chrysalis, from which they will later emerge as adult moths, mate, and begin laying eggs all over again.
Trees are quite resilient, even against the ravages of a total defoliation across multiple years, according to Ricard, so long as the defoliation isn’t compounded by additional stress such as drought. But that’s not a hard and fast rule; some trees just won’t make it.
“There’s going to be some mortality, no question about it,” Ricard said.
Most trees that are defoliated will grow a second set of smaller leaves later in the season, but not always.
Ricard said the egg masses appear to be fairly evenly distributed across the state, so it’s likely the damage will spread beyond heavily forested, rural areas and reach into the suburbs. But even homeowners who don’t see egg masses on their trees should be concerned, because gypsy moths, dangling from fine silk-like threads, can blow in the wind up to 12 miles to sail from one forest canopy to the next.
“Even if you have no egg masses on your property, if there are other trees within 12 miles of you, you’re probably going to have some level of defoliation.”
There are a couple of naturally occurring pathogens that could adversely impact the vigor of the gypsy moth census, including a fungus known as entomophaga maimaiga. The fungus is airborne and also easily spread from one caterpillar to another, but unless there is plenty of rain during the early part of May, it’s unlikely the environmental conditions will be favorable for concentrations of entomophaga maimaiga to reach levels that are significantly toxic to the caterpillars.
A virus known as NPV, or nucle-opolyhydrosis, may also kill off gypsy moths in significant numbers before they pupate. In their egg stage, some gypsy moths will be killed and eaten by predatory flies and wasps.
But it may take a perfect storm of pathogens and predators to make a significant dent in this season’s attack of creepy crawlers.
So what’s a besieged property owner to do?
If you live in a heavily forested area where everybody has trees – not much, according to Ricard.
There are a number of products on the market that contain a bacteria known as bacillus thuringiensis, or BTK, that can be sprayed directly on foliage. The substance causes caterpillars to sicken and die as a result of massive gastrointestinal distress. Such products might be useful for homeowners who are trying to save one special tree or a favorite orna- mental, but they’re impractical for homeowners to use on a large scale.
Ricard said property owners can also wrap duct tape, sticky-side out, around the base of their trees to discourage caterpillars from climbing them. Typically, the stickiness of duct tape lessens after it’s been exposed to the elements for a while, but the gum factor can be freshened up with tree-banding glue, which is available at nurseries and hardware stores.
There isn’t much time left, but property owners can check their trees for egg masses now. They can be removed manually or incinerated with a blow torch.
For food foliage, the preferred diet of gypsy moths consists of oak, aspen, apple, birch and willow trees. If the population of bugs is dense enough, they’ll settle in a tree and strip it of foliage.
If they exhaust the supply of their favorite leafy greens, they’ll move onto less desirable species such as maple, elm, hickory, larch and sassafras. Finally, they’ll go after the needles on certain pine trees if that’s all that’s left, according to DEM.
Generally, gypsy moths avoid ash, black walnut, catalpa, red cedar and flowering dogwoods, among others.
European natives, gypsy moths have been present in the environment since they were first introduced into Massachusetts in the 1860s by an amateur entomologist from France named Etienne Leopold Trouvelot. He was trying to breed a new kind of silkworm, but some of the gypsy moths escaped into the woods behind his house in Medford and they’ve been here ever since. Today they’re prevalent throughout much of the Eastern U.S., as far north as Quebec and as far west as Oregon.
Though they suspect a number of variables are at play, entomologists don’t completely understand what causes the boom-and-bust cycle of gypsy moth demographics. They just know that it booms and busts at intervals that are seemingly random.
Ricard’s observations bear out the pattern. He said state foresters have been counting egg masses since 1985. From 2007 to 2013, state forester searching for egg masses on the test plots found none. They showed up again in the fall of 2014, with just nine egg masses in total.
Suddenly, in 2015, the test plots yielded 3,500 egg masses, the first indication that another boom was on the way.