BAGWORM
DESCRIPTION
The Bagworm is a perennial insect pest of Arborvitae,
Juniper, Pine, Spruce and many other evergreen species.
It may also attack certain deciduous trees such as Black
Locust, Honeylocust and Sycamore. The insect is most
easily recognized by the case or bag that the caterpillar
forms and suspends from ornamental plants on which it
feeds. The bag is made of silk and bits of host leaves
and twigs. These materials are interwoven to disguise and
add strength to the case. When the caterpillar is mature,
the bag may be 30-50 mm in total length. Young larvae
hatching from the eggs are approximately 2 mm long,
glossy black on the back and dull amber on the
undersurface of their bodies. Full grown larvae are dull,
dirty gray and splotched with darker markings toward the
head. Mature larvae are about 18-25 mm long. The adult
female bagworm is worm-like. It lacks eyes, wings,
functional legs and mouth parts. She never leaves the bag
that she constructed as a larva. The adult male is sooty
black and moth-like with transparent wings that are
nearly devoid of scales.
LIFE CYCLE
Bagworms overwinter as eggs inside the female bag. Female
bagworms lay 500-1000 eggs in each bag during the
previous fall. Eggs will start hatching from late May
through early June. Upon hatching, the young larvae crawl
out of the bag and start to feed and construct silken
shelters over their bodies. As the larvae grow over the
eight to ten week feeding period, they continue to
enlarge the exterior of their bags with pieces of
foliage, bits of bark, or other plant parts. Feeding and
development usually continue until August. Mature larvae
loop strands of silk around a twig and become firmly
attached. After the top of the bag is closed, larvae
reverse their position in the bags so that their heads
face downward. They then change into the pupal (resting)
stage and remain in this life stage for about 4 weeks.
During September and early October, the males leave their
cases and fly to bags containing females where mating
takes place. Each mated female deposits a mass of eggs
inside her bag. She crawls out of the bag after laying
eggs, drops to the ground and dies. The eggs overwinter
inside the bag until the following Spring. There is only
one generation a year in Pennsylvania.
DAMAGE
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 such as Sycamore,
Willow and other deciduous trees, usually refoliate after
heavy defoliation. Unfortunately, Bagworm infestations
generally go undetected until damage is complete, and the
large bags of these insects are very conspicuous. Early
detection of an infestation requires careful examination
of host plants for the presence of small Bagworms
attached to the leaves or needles.
CONTROL
Non-Chemical
Bagworms may be controlled on small shrubs and trees by
handpicking or cutting the bags from infested plants
during late Fall, Winter or early Spring, before egg
hatch. Dispose of the bags so that this pest will not
reenter your landscape. A number of natural enemies
attack the larval and egg stages of the Bagworm.
Apparently, natural enemies are responsible for Bagworm
population changes from year to year.
Chemical
When Bagworms are too numerous to handpick, an
insecticide application may be indicated. Formulations of
acephate (Orthene), carbaryl (Sevin), cyfluthrin (Tempo)
and malathion (Malathion) are labeled for Bagworm
control.* Treat after eggs hatch and caterpillars are
small during early to mid June. Follow all label
directions for specific information on host plant label
clearance, phytotoxicity information, safety precautions
and dosage information.
* See Woody Ornamental Insect, Mite and Disease Management, The Pennsylvania State University (2005) for more details.
WARNING: Pesticides are poisonous. Read and follow directions and safety precautions on labels. Handle carefully and store in original labeled containers out of reach of children, pets and livestock. Dispose of empty containers right away , in a safe manner and place. Do not contaminate forage, streams or ponds.
For professional assistance
with tree and shrub problems,
contact Keystone Tree Experts at (215) 348-4444.
