The bagworm is an occasional pest on evergreen and deciduous trees and shrubs in southern Iowa. Infestations are rare north of Interstate Highway 80. The most commonly attacked host plants are arborvitae, red cedar and other juniper species, black locust, maple and sycamore. Over 128 plant species have been reported as host plants for bagworm. Attacked plants usually are partially defoliated, weakened and rendered unsightly. It is not uncommon for complete defoliation to occur.
The most noticeable sign of a bagworm infestation is the presence of tough silken bags on the branches or foliage. Each caterpillar produces an individual protective silken bag or case around its body. With its head and legs free, it is able to move about the plant as it feeds on the foliage. As the larva grows it increases the size of its bag and incorporates into it bits of twigs and leaves for strength and camouflage protection. The larva will spend its entire life within its bag. Larvae first appear about mid-June and are full grown by mid-August.
Bags of mature larvae are approximately 2 inches long. When the larva stops feeding the bag is attached firmly to a twig and sealed shut. The larva pupates within it. By mid-September the bagworm has transformed to the adult moth stage. Female moths lack wings, eyes, antennae, legs and functional mouthparts. They remain inside the larval bag. Adult males emerge from their bags and fly about infested plants seeking out females. After mating, the female lays between 500 and 1,000 eggs within her bag, and then dies. The eggs remain within the bag throughout the winter until they hatch the following spring. There is one generation each year.
Our weather and natural enemies such as birds, insect predators and parasites are effective in controlling bagworms most of the time. If bagworms are present the cheapest method of control on small trees and ornamentals is to handpick the bags during the winter or soon after the eggs hatch and while the bags are small. If handpicking is not practical spray infested plants as soon as the eggs hatch and small larvae begin feeding. Chemical control becomes less effective as the season progresses because of the increased size of the larva and its bag. Insecticides that can be used against the bagworm include Bt (Bacillus thuringiensis), Sevin, permethrin, Orthene, or malathion. Apply according to label directions.
Adopted from “The Bagworm in Missouri” (G7250)
By Bruce A. Barrett, Department of Entomology
University of Missouri-Columbia
Revised July, 2004
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