Jul. 2—There have been many reports this week about bagworms covering landscapes across Pontotoc County and surrounding counties. The common bagworm, Thyridopteryx ephemeraeformis, is found most frequently in its larval form, feeding on trees from within a silken bag it constructs from foliage and other plant tissues (hence, the insect’s common name). Adult males are small, clear winged moths with a black, hairy body and a wingspread of about 1 inch. Adult females are wingless, have no functional legs, eyes, or antennae, and are almost maggotlike in appearance. The females body is soft, yellowish white, and practically naked except for a circle of woolly hairs at the posterior end of the abdomen. Mature larvae have a dark brown abdomen and the head and thorax are white, spotted with black. They are about 1 inch long. Both larvae and adult females are found in silken bags on the host plants.

Although the larvae (caterpillars) feed on the leaves of more than a hundred kinds of trees, the more common hosts are eastern red cedar, other junipers, and arborvitae. Other hosts sometimes damaged include pines, spruce, bald cypress, maple, boxelder, sycamore, willow, black locust, oaks, and roses. The bagworm has been recorded on 128 different plant species in various parts of the United States.

Symptoms: Bagworm larvae damage their hosts by feeding on the foliage. Heavy infestations can completely defoliate small plants. Defoliation usually kills hosts such as red cedar and other junipers. Broadleaf hosts are not killed but are weakened and become more susceptible to borers and diseases.

Life Cycle: The overwintered eggs (in the year old female bags) begin to hatch in late April or early May and the young larvae begin to feed and construct bags immediately. The first evidence of an infestation is normally a small bag, about 1 /4 inch long, standing almost on end. As larvae grow, silk and fragments of the host plant foliage are added to the bag until it reaches 1 1/2 or 2 inches long. When larvae are mature they fasten the bag to a plant stem with silk. Pupation occurs in the bag in August and males emerge in late August and September. They engage in a mating flight in search of the wingless females still inside their bags. After mating the female lays several hundred white eggs inside her old pupal case, drops from the bag, and dies. There is one generation per year.

Management: Regardless of which season bagworms are encountered, infestations can be reduced or eliminated by removing bags by hand. The removed bags should be destroyed or discarded immediately, even in the winter because overwintering eggs within each bag remain viable. Bagworm cases can be disposed in the trash, but do not place them in compost piles or bins. When larvae become active in spring, bagworms can still be removed by hand if they are not too abundant, and the infested tree isn’t too tall. Do not climb trees or ladders to reach upper canopies just to remove bagworms. Call an International Society of Arboriculture (ISA)-certified arborist!

There are several naturally occurring parasitic and predatory wasps that attack bagworms. Certain fungal pathogens may play an important role in natural control of bagworms as well. The activity of these natural enemies at least partially explains the fluctuation in bagworm populations observed from year to year.

Chemical controls are most effective if applied early when larvae are small. In Oklahoma, it is normally a good practice to make insecticide applications by early June. Products containing Bacillus thuringiensis subsp. kurstaki (Bt), a bacterium that produces a toxin specific to caterpillars, are reported to provide good control of bagworms. Other effective reduced-risk products include those that contain the active ingredient spinosad (spinosyns A & D). Both active ingredients are most effective against small, young larvae, and they lose their effectiveness as larvae mature.

Mid to late season, large, older larvae are not as susceptible to Bt and spinosad as young larvae. Thus, bagworms must be sprayed with broad-spectrum, contact insecticides. Homeowners can look for products containing the active ingredients carbaryl (Sevin) or malathion that are labeled for caterpillar control on ornamental plants. As mentioned above, an ISA-certified arborist should be hired to combat bagworm infestations on large trees with tall canopies. Contact your county extension office for assistance with locating an ISA-certified arborist in your area.