Gypsy Moth Caterpillar Population Expected To Plummet This Year

May 4, 2018

Rhode Island environmental officials are expecting the gypsy moth caterpillar outbreak to finally end this year. 

The caterpillars feed on leaves and have defoliated hundreds of thousands of acres of forest throughout the state. Defoliation weakens trees and can eventually cause them to die. 

Each fall and early winter, members of the Department of Environmental Management's Forest Health Program count clusters of gypsy moth caterpillar eggs - or egg masses -  at 142 designated plots throughout Rhode Island.

The number of egg masses in the state has been climbing for the past few years. 

During their count in 2016, officials found more than 36,000 egg masses, which can hatch tens of millions of caterpillars.

However, last year DEM found only about 1,000 egg masses, the lowest since 2014 when 44 were recorded. 

"I am anticipating that there’s going to be some local infestations with spotty defoliations but that the caterpillars will die off this year, and we will return to just to a population (of caterpillars) resident in the state not noticed by anybody," Paul Ricard, coordinator of DEM's Forest Health Program, said. 

Ricard said the decline is due to more rain last spring, which activates a fungus that naturally controls the gypsy moth population.

He said a virus that naturally occurs within the environment also helps keep the caterpillars' numbers low. 

To protect trees on your property, Ricard recommends treating the leaves with a pesticide called Btk.