Out
On A Limb / May 2006
In the Bag
She may live wrapped in silk, but Thyridopteryx ephemeraeformis is seriously inelegant. Bug-ugly and destructive, the bagworm is capable of rapid buildup and extensive defoliation.
Bagworms are caterpillars that overwinter as eggs inside silk cocoons, each containing from 500-1,000 eggs. Eggs hatch from late May through early June and the caterpillars have an 8-10 week feeding period. By mid-August, the larvae are mature and often move to a sturdy branch where they attach the bag firmly with a strong band of silk.
The obnoxious guests occur in the eastern US from New England to Nebraska and south through Texas. The larvae prefer arborvitae and red cedar but other cedars, other conifers and deciduous trees are attacked, too, including pine, spruce, juniper, willow, sycamore, apple and maple, elm, poplar, oak and birch. Bagworms will also damage hemlock, box elder, willow and linden.
Easily recognized by the spindle-shaped case or bag the caterpillar forms, the insect is suspended from the ornamental plants on which it feeds. The bag is made of silk and camouflaged with bits of leaves, bark, twigs and other debris, interwoven to disguise and add strength to the case.
When disturbed, the larva pulls its head into the bag and holds the opening closed.
Bagworms overwinter as eggs inside the female bag. Female bagworms lay 500-1000 eggs in each bag during fall and their eggs start hatching from late May through early June. The adult female is worm-like, with no eyes, wings, functional legs or mouth parts. She never leaves the bag she constructed as a larva. Upon hatching, the young larvae crawl out of the bag and start to feed, constructing silken shelters over their bodies. As the larvae grow, they continue enlarging the exterior of their bags with bits of bark or other plant parts. The completed bag is 1-2 inches long. Feeding and development usually continue until August.
Mature larvae may stay on their host plant or drag their bags some distance before firmly attaching the bag for transformation into the adult stage. They loop strands of silk around a twig and become firmly attached. In early fall, males leave their cases and fly to bags containing females for mating since bagworm females cannot fly. The mated female deposits a mass of eggs inside her bag, crawls out of the bag, then drops to the ground and dies. The eggs overwinter inside the bag until the following spring.
Bagworm larvae injure plants when they feed on needles and leaves. Young caterpillars feed on the upper epidermis of host plants, sometimes leaving small holes in the foliage. Damage by mature larvae is especially destructive to evergreen plants. Trees will have increasing leaf damage from defoliation from June to late July and August with stripping of leaves most noticeable in the uppermost parts of trees and shrubbery.
The band of silk that larvae wrap to attach may girdle the branch as it grows, resulting in dead branches years later. Crowded larvae may eat the buds on conifers causing branch dieback and dead areas. Excessive defoliation may cause plant death the following season but even moderate defoliation is damaging and unsightly.
Sycamores, willows and other deciduous trees usually refoliate after heavy defoliation but bagworm infestations generally go undetected until damage is complete, leaving the grim insect bags glaringly apparent.
Early detection of an infestation requires careful examination of trees for the presence of small bagworms attached to leaves or needles.
The non-chemical method of control is handpicking them off or cutting and destroying the bags from infested plants in early spring, late fall or during winter, before eggs hatch. (The silk band should be cut when removing bags from a plant.)
When picking is too disgusting, consider insecticide formulations of acephate (Orthene), carbaryl (Sevin) or cyfluthrin. Treat trees after eggs hatch and while caterpillars are small, from early to mid June, since small larvae are more susceptible to insecticides. Larger larvae and molting larvae are not easily killed. Look for insecticides with some residual to make sure bagworms bug out. PL
Copyright © 2005-2006 A Woman's View. All rights reserved.
Femme Fair 2006
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