Sizing up the moth threat
With massive tree defoliation forecast, recent rainy spell may have put damper on the local caterpillar population
WOONSOCKET — After a state forester led an informational session on the coming gypsy moth invasion in northern Rhode Island last month, the takeaway for one listener was, “Pray for rain.”
That’s because damp, wet conditions are conducive to naturally occurring pathogens that can be deadly to the voracious leaf-eaters, which began hatching across the state in record numbers a few weeks ago.
Now that the hoped-for rain has arrived, has it put a damper on the caterpillar boom?
“It’s too premature to say that,” says Cathy Sparks, assistant director of natural resources for the state Department of Environmental Management. “The situation appears to be favorable but until I actually see it I’m not inclined to speculate.”
State foresters have been warning residents to brace for widespread tree defoliation this season, predicting that more than 400,000 acres of woodland could be affected, from the burbs to the boondocks. The estimate comes from a survey of forest test plots around the state that revealed about 35,000 gypsy moth egg masses per acre, or 10 times the number of the fuzzy, brown patches observed on tree trunks prior to last summer’s defoliation cycle, when gypsy moths stripped leaves from more than 226,000 acres of woodland.
Sparks says the conditions are promising for a gypsy moth population bust, but it’s likely the creatures will do some significant damage to trees before the natural pathogens start killing them off.
Many property owners in northern Rhode Island and other parts of the state have already seen gypsy moths, which began hatching two or three weeks ago. At this point, the caterpillars are little more than thin, wriggly squiggles – perhaps a half inch long or less.
In some areas, they’re just hatching, or about to.
“In the northern areas, they’re still coming out now ‘cause the weather was cooler,” says Tony DeJesus of Big Blue Bug Solutions in Providence. “Southern
areas and in the East Bay hatched a little bit earlier because they had slightly warmer temperatures.”
Like Sparks, DeJesus said his technicians in the field haven’t been able to detect a significant impact on the gypsy moth population from the weather.
“We haven’t as of yet, but that doesn’t mean it’s not happening out in the forest and stuff like that,” he said. “It does take a while for these pathogens to build up.”
The hope is that the comparatively wet conditions this spring will foster the growth of a fungus called entomophaga maimaiga and the viral agent NPV, or nucleopolyhedrosis. Both are deadly to gypsy moth caterpillars, but Sparks says the bugs don’t usually get sick until they’re closer to the pupation stage of their life cycle, when they form cocoons. Later, they emerge as adult moths, mate and start laying eggs all over again.
But Sparks stops short of making any predictions and strikes a cautionary note about overstating the case for a wet spring. Certainly, she says the springs of 2015 and 2016 were much drier than usual – meteorologists deemed much of Rhode Island and Massachusetts to be afflicted by some degree of drought. Those conditions may have helped drive the explosive growth of the gypsy moth population to levels that have not been seen since the mid-1980s.
By comparison, Sparks says this spring’s rainfall checks in closer to normal than aboveaverage.
If the worst-case scenario develops, however, residents across the state – more so in heavily forested zones – can expect to see areas where trees are completely defoliated by gypsy moths. The insatiable insects will feast on leaves down to the veins, zoning in on their preferred greens first, including oaks, maples and other hardwoods. The creepy crawlers will move on to certain fir trees, stripping them of needles, if they live long enough to exhaust the supply of their favorite foods.
Foresters recommend banding trees with duct tape, sticky side out, to prevent caterpillars from climbing into the leaf canopy. But in heavily forested areas and backyards dense with trees, tape is a stopgap at best because the light, furry wrigglers can hitch a ride on the wind from tree to tree, easily covering more than 10 miles during the caterpillar stage of their lives, which can last until July in this part of the country.
Homeowners who want to save a few small ornamentals or fruit trees might be better off trying any of a number of commercially available products that contain a bacteria known as bacillus thuringiensis, which is also fatal to gypsy moths – and many other caterpillars. Thuricide is a common brand that’s available at many hardware stores and nurseries. It can be purchased in concentrate or pre-mixed, in a container that can be attached to a garden hose for long-distance spraying.
Citing the exorbitant cost of nipping a mass defoliation in the bud, as well as the harmful effects on beneficial insects, DEM announced weeks ago that it would not embark on an aerial spraying program to kill gypsy moths. Many homeowners are turning to private companies and arborists to save their trees. Business is apparently booming. “It’s crazy,” said a woman who answered the phone at Stanley Tree Service in North Smithfield.
Most trees that are defoliated will grow a second set of smaller leaves later in the summer and return to a normal growing pattern in successive years. Foresters say healthy trees can generally withstand multiple years of defoliation, but there are no guarantees.
While it’s already possible see tiny holes in leaves where juvenile caterpillar larvae have begun munching away, some aggrieved property owners are also experiencing another nuisance condition as a result of coming into contact with the tiny bugs: skin rashes.
Some individuals will develop blotchy, red patches on their skin because they’re allergic to a toxin contained in the hollow hairs on the bodies of the caterpillars, according to Sparks.
“I’m one of them,” says the assistant director, who treats herself with Benadryl lotion. “Very uncomfortable. Very itchy.”
About a week ago, suspicions initially turned to mouse droppings in the basement of Veterans Memorial Elementary School in Central Falls when more than a dozen children came down with rashes. Afew days later, officials decided it was more likely the children had come into contact with gypsy moth hatchlings on trees in an area of the schoolyard where they had been playing.
Experts say gypsy moth rashes can last up to several days and the itching can usually be controlled with over-the-counter products, but there are reports of more severe cases that were treated by doctors with prescription-strength cortisone or other steroids.