Too late, baby, now it's too late

            When Rhode Island House Minority Leader Patricia Morgan sent a letter to Governor Gina Raimondo on May 2 asking that a plan be developed and launched to eradicate gypsy moth caterpillars throughout the state, she was likely responding to the highly-visible emergence of masses of tiny caterpillars from their eggs that week. Her reaction could be considered understandable, since just walking outside in proximity to trees left many residents with specks of moth larva clinging to their clothing.

            According to one expert, however, a statewide eradication program is unnecessary and may even backfire. And by the time the caterpillars hatch, it’s already too late to plan and

implement an eradication program.

            Heather Faubert, an entomologist who directs the Plant Protection Clinic at the University of Rhode Island, agrees that the state is in for another year of forest defoliation that will likely be similar to the 230,000 acres that were defoliated by gypsy moth, winter moth and forest tent caterpillars in 2016.

            “But by the end of this growing season, the population of gypsy moth caterpillars will crash and they won’t be a problem next year,” said Faubert, who monitors caterpillar populations for the state’s fruit growers. “The diseases that usually control the population start spreading when the population is high and when we have wet weather in May. We’re having a wet May, so I expect the population to crash all on its own this year.

            “But not before the gypsy moths that are already here do quite a bit of damage,” she added.

            She said that the only way to eradicate gypsy moths throughout the state would be through aerial spraying of an insecticide.

            “There’s no other solution,” Faubert said. “And it would need to be done by the third or fourth week of May. Logistically it’s not even possible to organize a spraying program that quickly.”

            She said that the usual insecticide used to kill gypsy moth caterpillars in aerial spraying is not available commercially and must be ordered by state governments in the autumn. The next best choice is one of the so-called Bt insecticides, which attack all caterpillars, not just gypsy moths, wiping out all moth and butterfly populations in the area sprayed.

            “There was opposition to aerial spraying in the early 1980s, and there would be a lot more opposition now,” said Faubert.

            Even if a plan were developed, the insecticide acquired, opposition quelled, and spraying took place during the most optimal time, Faubert believes it would likely prolong the gypsy moth outbreak.

            “If we spray, there will certainly be lots of pockets of places that don’t get sprayed,” she said. “And the chemicals are never 100 percent effective. So if, say, 15 percent of the caterpillars in the state survive, the caterpillar population won’t be dense enough to spread the diseases that usually kill them off, so we’ll be facing the same problem next year.”
          Unfortunately, while the prognosis for next year is good, the state is in for a rough summer this year. Even if May remains wet and the diseases spread throughout the caterpillar population as Faubert predicts, the caterpillars won’t die until they are full grown and have already eaten a huge number of leaves.

Sadly, it’s not just the trees that will be affected.

            A number of local ecologists have noted that forest defoliation allows more direct sunlight onto the usually shaded forest floor, which means sun-loving invasive plants have a greater opportunity to spread through the forest; shade-loving frogs and salamanders may struggle to remain cool and moist; and some birds and small mammals may find it more difficult to hide from predators.

            The increased sunlight through the trees also means that the water temperature in many forested streams and ponds will likely increase, resulting in a reduction in dissolved oxygen levels in the water that can cause distress in sensitive aquatic species.

            On the other hand, URI ornithologist Peter Paton said that several species of migratory songbirds that feast on gypsy moth caterpillars, especially black-billed and yellow-billed cuckoos, will likely benefit from the abundance of caterpillars in the forest this year. Birdwatchers in the area noticed an unusually large number of cuckoos last year, and this year’s population should be even greater. Indigo buntings, which prefer open habitat, also tend to experience short-term increases when trees are defoliated.

            David Gregg, director of the Rhode Island Natural History Survey, said that he found unusually healthy populations of some spring wildflowers in Snake Den State Park in Johnston this month, which he attributes to the defoliation from last year’s gypsy moth outbreak.

            “Most forest floor plants are adapted for growing in the dark of the forest canopy, but some are still capable of growing faster and better if they have more light,” he explained. “So when there's defoliation, they have a good year. That means they put away a lot of food into their roots and have a good next spring.

            “But,” he added, “most of the rest of the gypsy moth news is bad.”

This article first appeared in Newport Mercury on May 23, 2017.