Defoliators
> Bagworm
Pest: Bagworm (Thyridopteryx ephemeraeformis (Haworth)
Order: Lepidoptera
Family: Psychidae
Host Plants:
In the northeastern United States, Thuja (arborvitae) and
Juniperus (juniper) are the two common host genera.
Description:
The larvae form "bags" or cases made from plant foliage
and silk and these may appear to be normal plant parts to the untrained
eye. Larvae will carry these cases while they defoliate the host
plant. Injury can be quite severe when populations are high. Complete
defoliation and plant death can result from the feeding activity
of this pest. Given that the female does not fly, injury usually
appears severe on one plant and then often radiates down a hedgerow
from that one initially infested plant to others.
Life Cycle:
Eggs over-winter within the female "bag" and hatch
around mid-June in southern New England. Newly hatched larvae will
disperse by crawling from the bag or they may balloon from the egg
hatching site a short distance. Larvae will begin to feed and then
construct the "bags" that they carry with them while they
feed into late summer. Pupation occurs in late September into October
in New England. Male moths will develop and appear moth-like but
females will forever remain larval-like in appearance by not developing
wings, legs or antennae. Males will seek out these females and mating
occurs with the female never leaving her case. Soon thereafter,
the female produces anywhere from 500-1000 eggs and then dies.
GDD: 600 - 3000
Management:
Given that this insect does not pupate until late September
into October it is usually killed by frost, in the larval stage,
in New England. It is not a "native pest" of this region.
In fact, bagworms are only a continuous problem starting at the
latitude that includes Maryland and ranging south to the Gulf of
Mexico. However, occasionally bagworm is a serious pest in southern
New England and it is due to several factors: New populations are
usually brought in on nursery stock from more southern states and
introduced into the landscape at planting time. They will cause
a certain amount of injury during that growing season and if that
region experiences a prolonged, warm autumn, the larvae will pupate
and mating will occur during the following year. Given that each
female can produce upwards to 1000 eggs, this pest can increase
in numbers exponentially for the next growing season.
Management Strategies:
If detected early, the few "bags" can be removed by
hand. Otherwise, Bacillus thuringiensis (B.t.) is
effective on younger larvae. Several chemical pesticides are also
labeled for this pest.
Images:
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Bagworm caterpillars within their cases made from plant foliage.
(R. Childs)
A close-up photograph showing a bagworm larva partially outside
its bag. (Deborah Swanson)
Dead foliage of an arborvitae displaying
the old gray bags of a recent past bagworm
infestation. (R. Childs)
A hedge of arborvitae that clearly displays the common dispersal
pattern of a bagworm dinfestation. (R. Childs)
A close-up of the Snailcase Bagworm. (R. Childs)
A close-up of the Snailcase Bagworm on a dime to show relative
size. (R. Childs)
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Defoliators
index:
Armyworm
Asiatic Garden Beetle 
Bagworm
Cankerworms
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Caterpillar Update
Eastern Tent Caterpillar
Fall Webworm
Forest Tent Caterpillar
Gypsy Moth
Japanese Beetle
Larch Casebearer
Lily
Leaf Beetle -
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Mimosa Webworm
Viburnum Leaf Beetle
Winter
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Winter
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