BAGWORMS
Bagworms are 1/8 to almost 2 inches long depending on age. The head and
forward parts are dark and hardened and the rest is paler and soft. Each
bagworm is covered by a bag made of white silk with bits of the host plant
spun onto the outer surface. The pupae are dark brown. Male pupae are slender
and female pupae are fatter. The pupal stage occurs inside the bag. Female
bagworms are wingless, legless and grub-like (they never leave the bag).
Males are small, brown hairy moths with dark wings that clear with age.
Eggs are spherical or oblong and about 0.8 mm by 1.0 mm. Eggs are found
in the mother's bag inside her pupal cast skins.
Bagworms occur throughout North Carolina. Bagworms have a very wide host
range but are usually associated with arborvitae or juniper. A single bagworm
does relatively little harm as it feeds on leaves. Excessive defoliation
may kill conifers within one or two seasons. Damage is most noticeable
in landscapes rather than woodlands. Occasionally, the silk band with which
the bagworms attach themselves to a twig before they pupate girdles the
twig as the twig enlarges. Winter is spent as eggs (500 to 1000) in the
mother's bag.
They hatch in May and June. The newly hatched larvae spin down on silken
threads and are blown about by the early spring breezes. Most of the larvae
land on the original host plant but some small worms may be "ballooned"
for some distance on the silk thread. Upon reaching a suitable host, the
worm begins to spin its bag and as it grows, it incorporates some of the
host plant foliage into the bag for camouflage. As the bagworms grows,
it enlarges the bag and adds fresh plant material to the outside. In August
the worms mature and molt into the pupal stage. The bag is firmly attached
by a sturdy silk band which the bagworms usually wrap around a twig. During
August and September, male moths emerge from their bags to mate. After
mating, females lay their eggs inside the pupal cast skins and die.
Apparently when the newly hatched larvae reach a plant which is different from its parents' host plant, these insects often have difficulty in adapting to it and may die or may produce only a few offspring. After several years of struggling to keep from going extinct, the population may hit on the right combination of genes for the "new" plant and "suddenly" the new plant is covered with bagworms.
Bagworms are parasitized by several kinds of parasitic wasps. A 2005 article by J.A. Ellis et al., reported that bagworm infested arborvitae (Thuja) plants in Illinois, surrounded by a high density of asters such as Shasta daisies, showed high rates of parasited larvae.
When practical, bagworms can be removed with scissors or a sharp knife. Insecticides are effective particularly when applied in June or early July when the bagworms are small and relatively sensitive. The following insecticides are labeled for bagworm control.| pesticide (Trade Name) | Formulation | Amount of Formulation |
|---|---|---|
| *acephate (Orthene) | 9.4 % emulsifiable concentrate | 3 tablespoons per gallon of water. |
| acephate (Orthene) | 75 % soluble powder | 1/3 pound per 100 gallons of water. |
| *Bacillus thuringiensis B.t.( Biotrol, Dipel) | 3.2 to 20 % | 1 to 4.5 teaspoons per gallon of water depending on label directions. |
| bifenthrin (Talstar) | 10 % wettable powder | 1 to 5 teaspoons per gallon of water. |
| *carbaryl (Sevin) | several formulations on the market; follow label directions. | |
| cyfluthrin (Decathlon) | 20 % wettable powder | 6 tablespoons per 100 gallons of water. |
| fluvalinate (Mavrik Aquaflo) | 22.3 % aquaeous suspension | 1/8 to 5/8 teaspoon per gallon of water. |
| *malathion (Cythion) | 56 % emulsifiable concentrate | 1-1/2 teaspoons per gallon of water. |
| permethrin (Astro) | 36.8 emulsifiable concentrate | 1/4 to 1/2 teaspoon per gallon of water. |
| spinosad (Conserve SC) | 11.6% emulsifiable concentrate | 3/8 teaspoon per gallon of water |
Recommendations of specific chemicals are based upon information on the manufacturer's label and performance in a limited number of trials. Because environmental conditions and methods of application by growers may vary widely, performance of the chemical will not always conform to the safety and pest control standards indicated by experimental data.Recommendations for the use of chemicals are included in this publication as a convenience to the reader. The use of brand names and any mention or listing of commercial products or services in this publication does not imply endorsement by the North Carolina Cooperative Extension Service nor discrimination against similar products or services not mentioned. Individuals who use chemicals are responsible for ensuring that the intended use complies with current regulations and conforms to the product label. Be sure to obtain current information about usage and examine a current product label before applying any chemical. For assistance, contact your county North Carolina Cooperative Extension Service agent.
J.A. Ellis et al., "Conservation Biological Control in Urban Landscapes: Manipulating Parasitoids of Bagworm with Flower Forbs", Biological Control 34(1), July 2005, 99-107.
Moore, Robert G. & Hanks, Lawrence M. (2004)
Aerial
dispersal and host plant selection by neonate Thyridopteryx ephemeraeformis
(Lepidoptera: Psychidae).
Ecological Entomology 29 (3), 327-335.