Pest Watch Bagworm

BIOLOGY: The adult female bagworm (Thyridopteryx ephemeraeformis) certainly doesn’t look much like a moth, since she has no wings, eyes, legs, antennae or functional mouthparts. In fact, her soft. yellowish white body never leaves the bag in which she has matured. The male moth, however, does fly. Black with clear wings spanning an inch, he leaves his own bag and flies to the female, where he mates and dies. The female then lays 500 to 1.000 eggs inside her bag before succumbing as well. The eggs overwinter inside the bag and hatch in late May or June in the middle Atlantic states. Native to a wide area of eastern North America. T. ephemeraeformis occurs from New England west to Nebraska and south to Texas and the Gulf Coast. The larvae feed on some 120 species of woody ornamentals-deciduous shrubs and trees as welt as conifers.

SYMPTOMS: Bagworms can easily be recognized by their cocoonlike cases, which are carried about by the larvae as they feed. Each larva constructs its bag of silk and bits of leaves and twigs cut from the host plant, so a bagworm’s appearance will vary from plant to plant. Although bagworms can be found feeding on black locust. buckeye, elm, honey locust, maple, sycamore, and willow, they are especially damaging to conifers such as arborvitae. cypress, hemlock juniper, and spruce, which can experience branch dieback or death from complete defoliation.

CONTROLS: Handpicking provides the most immediate relief. Removed bags can be dropped into a container of soapy water. Spraying with Bacillus thuringiensis (Bt) in June after the eggs have hatched and the young larvae are starting to feed is also an effective control. Bagworm sex pheromone traps set up in August will capture male moths seeking females and reduce future bagworm numbers. Unfertilized eggs will not hatch. Broad-spectrum pesticides should be avoided, as most are toxic to the ichneumon and chalcid wasps that are the natural parasites of bagworms.

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