GYPSY MOTH OUTBREAK IN CT? Scientists are concerned about this summer

Widespread gypsy moth activity and some tree defoliation has been detected this summer across areas of Connecticut, according to the Connecticut Agricultural Experiment Station (CAES).

Reports of activity have been most notable in New Haven, Middlesex, and parts of Hartford and New London counties.

In 2014, aerial surveys in late summer and early fall by CAES found relatively little gypsy moth defoliation — with about 1,337 acres impacted, mostly in New Haven County. But due to a very dry spring in 2015, there was no early control of the gypsy moth by the gypsy moth fungus Entomophaga maimagia.

Moisture is required for the fungus to infect the gypsy moth larvae (caterpillars), and little or no precipitation was available for the fungus to provide control of young caterpillars.

Limiting the moth population

With current rains, however, caterpillar mortality from the fungus is being observed. ”It is likely that this pathogen will knock back the gypsy moth population and help prevent a possible large outbreak in 2016 ,” said Kirby Stafford, the state entomologist.

The impact of the fungus on any gypsy moths in 2016 will be dependent on weather conditions in May and early June of next year, CAES officials said.

Gypsy moth detected here in 1905

The gypsy moth was first detected in Connecticut in Stonington in 1905.

The high-level gypsy moth activity this year shouldn’t mark a return to multiple years of widespread gypsy moth defoliation and the tree mortality experienced in the early 1980s. In 1981, 1.5 million acres were defoliated in Connecticut.

Christopher Martin, forestry director at the Connecticut Department of Energy and Environmental Protection, noted that in general, “partial or even complete defoliation of a tree in any one year does not mean the death of the tree. Healthy trees can tolerate some defoliation.”

Fungus kills caterpillars, limits moths

During a large outbreak in 1989, scientists at CAES discovered the entomopathogenic fungus Entomophaga maimagia was killing the caterpillars. This fungus has been the major agent suppressing gypsy moth activity since then.

However, the fungus is not expected to prevent all outbreaks and occasional high activity and outbreaks can continue to occur, particularly in years with little rainfall during the spring and early summer.

The last outbreak of gypsy moth activity in Connecticut was in 2005 and 2006. In 2005, gypsy moth caterpillars caused 64,273 acres of defoliation, mainly in Middlesex County.

A more widespread outbreak in 2006 caused 251,946 acres of defoliation, largely in Middlesex, New Haven, and New London counties.  It was eventually brought under control by the fungus and the arrival of early summer rains; a pattern similar to this year.

Up to 1,000 eggs per mass

There is only one generation of the gypsy moth each year. Caterpillars hatch from the buff-colored egg masses in late April or early May. An egg mass may contain 100 to more than 1,000 eggs laid in several layers.

A few days after hatching, the quarter-inch long caterpillars will ascend the tree and begin to feed on new leaves. These young caterpillars deposit silk trails as they crawl and, as they drop from branches on these threads, may be distributed on the wind.

Larger caterpillars generally crawl up and down tree trunks and feed mainly at night. They seek cool, shaded protective sights during the day. However, under outbreak conditions with dense populations of caterpillars, they may feed continuously day and night and crawl at any time.

Turning into a moth

The caterpillars generally complete their feeding sometime around the end of June and the first of July, and seek a protected place to pupate and transform into an adult moth in about 10 to 14 days.

Male moths are brown and can fly. The female moths are white and cannot fly. The female moth will lay a single egg mass and die. These eggs will pass through the winter and larvae will hatch the following late April or early May.

Destroying egg masses

It is past time for management or treatment options to control the gypsy moth this year. This fall, one control measure would be to remove and destroy egg masses, if any, found on tree trunks, decks, vehicles, outdoor furniture and other locations around the property before the larvae hatch next spring.

The difficulty is that many egg masses may be located in inaccessible areas (such as being high in the trees).

While there are a number of insecticides labeled for the control of gypsy moth on ornamental trees and shrubs, they need to be applied early in the season and thorough coverage of the treated trees by a licensed arborist is necessary for good control.