March 21, 2016

Early detection of Gypsy Moths and Tent Caterpillars

by Toni Leland

Gypsy Moth Caterpillar (Lymantria dispar)
Gypsy Moth caterpillar
March isn't exactly gardening season in New England, but it's a good time to scout your property for the egg cases of the Gypsy Moth (Lymantria dispar). A report from the Connecticut Agricultural Experiment Station (CAES) indicated that a huge outbreak of gypsy moth activity in mid-2015 could indicate another large emersion in 2016, if conditions are optimum. Gypsy moth infestation has the potential for disastrous results. In 1981, 1.5 million acres were defoliated in Connecticut; in 2006, over 250,000 acres were attacked in Middlesex, New Haven, and New London counties.

Early detection of egg cases is one step toward eradicating this pest from our own gardens. In March, the fuzzy, buff-colored egg masses are easily seen on trees, decks, vehicles, or outdoor furniture. Time is critical, as these masses may contain from 100 to 1,000 eggs. The caterpillars will hatch in late April or early May, after which the quarter-inch long caterpillars will begin to feed night and day on newly emerging leaves.

Preferred hosts include oak, white birch, gray birch, apple, willow, linden, basswood, hawthorn, sweet gum, and aspen, but other species are not immune. (UCONN Extension Home & Garden Center Fact Sheet)

Gypsy Moth Female (Lymantria dispar)
Gypsy Moth Female
Fill a small container with soapy water and carry it with you as you search out the egg masses. When you find one, scrape it off into the water. Leave the container overnight before dumping. If an egg mass falls to the ground while you're scraping, be sure to retrieve it; the eggs will hatch on the ground as easily as on the tree.

At the end of June or first of July, the caterpillars pupate for 10 to 14 days, after which the adult moths emerge. Males are brown and can fly. Females are white and cannot fly. If you see a female, destroy it.

Tent Caterpillars (Malacosoma americanum)

Tent Caterpillar (Malacosoma americanum) nest
Tent Caterpillar nest
Unsightly web nests covering the crotches of host trees are the signal that the tent caterpillars have hatched. This species has been recorded since Colonial times and appears in outbreaks every several years. For home gardeners with fruit trees, catching these pests early is important. Tents should be removed in early spring and destroyed.

Tent Caterpillar (Malacosoma americanum) egg caseFavored hosts include wild cherry, apple, and crabapple, but the insects may also be found on hawthorn, maple, cherry, peach, pear, and plum.

Tent Caterpillars (Malacosoma americanum)The tent caterpillar moth lays 150 to 400 eggs which will hatch in early March to coincide with buds opening. The mass of caterpillars stay together, spinning a tent in the crotch of the tree. As they grow and foliage is eaten, they extend the size of the tent to enclose newfoliage. At about 6 weeks, they are full grown and will wander from the nest searching for a place to spin a cocoon.

Tent Caterpillar (Malacosoma americanum) female moth
Tent Caterpillar female moth
Three weeks later, adult moths emerge and repeat the cycle.

NOTE: The tent caterpillar is often confused with fall webworms (which also spin a nest, but at the tips of branches), but the two are different species with different habitat and cycles.

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