Michigan State University Extension
Ornamental Plants plus Version 3.0 - 00001714
11/12/99
Caterpillars
Most of the leaf-chewing larvae of butterflies and moths
can be grouped together and referred to as caterpillars.
They are soft-bodied except for a hard head capsule and
have three pairs of thoracic legs and two to four pairs of
fleshy abdominal prolegs. Caterpillars come in various
sizes, shapes and colors. They may chew holes in leaves
or chew inward from the leaf edge. Some caterpillars are
hairy, while others are smooth-bodied and mimic twigs.
Most have a protective coloration that helps them blend
into the background of twigs and leaves.
Several species of caterpillars can feed on shade trees
and ornamentals in the north central states, but few
commonly cause significant levels of defoliation. Most
caterpillars occur chronically at non-damaging levels and
are damaging only rarely. Problems one season often are
not followed by problems the next year.
Because the great majority of feeding by a caterpillar is
done during the latest larval stages, defoliation may
appear to occur very suddenly. Often problems are not
detected until feeding is nearly over and treatments are
no longer of benefit. To detect potential problems early,
watch for the small larvae and the early phases of leaf or
needle feeding. In some situations, the pelleted
excrement (frass) of the young caterpillars on the ground
may tip you off to an infestation developing within a
tree.
Bacillus thuringiensis (Dipel, Thuricide), a microbial
insecticide that is exceptionally safe to use, is
effective against most caterpillars if you apply it so
that the insects ingest it.
Apply insecticides against caterpillars that make
protective structures (fall webworms, leafrollers, etc.)
shortly after the insect eggs hatch. Treatments made
later will generally fail to reach the insect.
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to commercial products or trade names does not imply
endorsement by MSU Extension or bias against those not
mentioned. This information becomes public property upon
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This file was generated from data base ZZ on 01/19/00.
Data base ZZ was last revised on 11/12/99.
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