Redhumped Caterpillar Integrated Pest Management

1. PEST NOTES Publication 7474
University of California
Statewide Integrated Pest Management Program
Agriculture and Natural Resources
June 2010
The redhumped caterpillar, Schizura
concinna, is found throughout much of
California. Although the climate of the
coastal regions usually doesn’t favor
development of destructive popula-
tions, it can be a serious problem in the
warm Central Valley. This pest most
commonly attacks liquidambar (sweet
gum), walnut, and plum trees, but you
also can find them on almond, apple,
apricot, birch, cherry, cottonwood, pear,
prune, redbud, willow, and others,
especially where insecticides applied
to control other pests have killed their
natural enemies.
IDENTIFICATION
The redhumped caterpillar has four
stages of development—egg, larva
(caterpillar), pupa, and adult (moth).
Adults lay eggs, which are nearly
spherical and pearly white to cream
colored, in groups of 25 to 100 on the
undersides of younger leaves (Fig. 1).
Caterpillars (Fig. 2) are 1 to 1 1
/2 inches
long when fully grown and have a base
color of yellow. Longitudinal white, red-
dish brown, or sometimes black stripes
mark the body. The head is usually or-
ange or brick red, as is the fourth body
segment, which is distinctly humped
and has two prominent, black tubercles
(spines). Each body segment also has
less distinctive black tubercles. Caterpil-
lars rest with their hind end elevated.
The pupa (Fig. 3) is reddish brown, a little
more than 1
/2 inch long, and enclosed in a
silken cocoon in the soil or in the layer of
organic debris covering the soil.
Adult moths (Fig. 4) have a wingspan of 1
to 1 3
/8 inches. The forewings are reddish
to grayish brown and often are darkest
along the hind margin. The hind wings
are off white to light gray or brown.
LIFE CYCLE
In autumn, caterpillars drop to the
ground and spin silken cocoons. They
remain inside the cocoons during win-
ter and transform into pupae in spring.
Moths begin emerging from pupae in
April and May. They mate, and each
female can lay more than 200 eggs.
The eggs hatch into tiny caterpillars
that feed, grow, and then drop to the
ground to pupate. There are often as
many as four or five generations per
year. Redhumped caterpillars seem to
be more abundant after a warm winter.
DAMAGE
Upon hatching, caterpillars feed in
groups on lower leaf surfaces and skel-
etonize the leaves (Fig. 5). As the larvae
become larger, they tend to disperse
and consume the entire leaf, leaving
only the tough, woody veins. When
infestation is light, larvae eat leaves on
only a few branches, but occasionally a
heavy infestation develops that defoli-
ates entire trees.
Most severe defoliation occurs during
the summer. Even if completely defo-
liated, trees that are otherwise healthy
usually recover. When defoliation oc-
curs on walnuts, the nuts are subject
to sunburn.
Integrated Pest Management for Home Gardeners and Landscape Professionals
Redhumped Caterpillar
Figure 1. Redhumped caterpillar egg
cluster.
Figure 2. Redhumped caterpillar larva.
Figure 3. Redhumped caterpillar pupa.
Figure 4. Redhumped caterpillar moth. Figure 5. Redhumped caterpillar feeding
on walnut showing a skeletonized leaf.

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MANAGEMENT
A number of parasitic wasps, includ-
ing Cotesia (Apanteles) species (Fig. 6)
and Hyposoter fugitivus (Fig. 7), use the
redhumped caterpillar as a host and
often provide effective natural control.
General predators including spiders,
lacewings, bigeyed bugs, and damsel
bugs also feed on eggs and caterpillars.
However, in some instances additional
control measures are necessary. The
simplest of these is to cut off the foliage
that contains caterpillars while the in-
sects are still young and active. At this
stage you’ll need to prune off only small
branches in order to destroy a large
group of caterpillars. Then either burn
the foliage or crush the caterpillars.
If you choose to use insecticides, choose
ones that are least toxic to the caterpil-
lar’s natural enemies. Bacillus thuringi-
ensis—which is sold as a variety of
products including Safer Brand Caterpil-
lar Killer or Greenlight BT Worm Kill-
er—is an effective spray for redhumped
caterpillar control. Bt, as it is commonly
known, is a bacterial preparation that
causes a diseaselike condition in many
types of caterpillars. They stop eating
several hours after feeding on a sprayed
leaf and die a couple of days later.
Spray with Bt after the first skeleton-
ized leaves appear. Bt is most effective
on the smallest caterpillars. Be sure the
caterpillars are present before spraying.
A complete coverage spray throughout
the entire tree is necessary for effec-
tive control. Bt won’t harm the natural
enemies of redhumped caterpillars and
other insects as the more toxic, broad-
spectrum insecticides do.
Another environmentally friendly insec-
ticide that controls redhumped caterpil-
lar is spinosad (Monterey Garden Insect
Spray). Like Bt, complete coverage of
leaves is required for effective control.
Experience has shown that sprays for
redhumped caterpillars often are ap-
plied too late to have any effect. Unless
many non-parasitized caterpillars are
present on trees, it’s best to delay spray-
ing until the next generation appears
and is feeding on the leaves. If you
find significant numbers of parasitized
redhumped caterpillar pupae, biologi-
cal control alone likely will control the
pest, and sprays shouldn’t be needed.
REFERENCES
Dreistadt, S. H., J. K. Clark, and M. L.
Flint. 2004. Pests of Landscape Trees and
Shrubs: An Integrated Pest Management
Guide, 2nd ed. Oakland: Univ. Calif.
Agric. Nat. Res. Publ. 3359.
Flint, M. L. 1998. Pests of the Garden and
Small Farm: A Grower’s Guide to Using
Less Pesticide, 2nd ed. Oakland: Univ.
Calif. Agric. Nat. Res. Publ. 3332.
Moore, W. S., and C. S. Koehler. 1981.
Redhumped Caterpillar—A Pest of Many
Trees. Oakland: Univ. Calif. Agric. Nat.
Res. Leaflet 21064. v
Figure 7. The parasite Hypersoter fugi-
tivus makes its cocoon within the body
of its caterpillar host. The heads of the
killed caterpillars are still visible.
Figure 6. The white silken cocoons next
to these redhumped caterpillars contain
pupae of the caterpillar parasite Cotesia
(Apanteles) species.

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TECHNICAL EDITOR: M. L. Flint
EDITOR: M. L. Fayard
ILLUSTRATIONS: Figs. 1-7, J. K. Clark.
This and other Pest Notes are available at
www.ipm.ucdavis.edu.
For more information, contact the University of
California Cooperative Extension office in your
county. See your telephone directory for addresses
and phone numbers, or visit http://ucanr.org/ce.cfm.
University of California
Agriculture and Natural Resources Program
Produced by UC Statewide
Integrated Pest Management Program
University of California, Davis, CA 95616
University of California scientists and other
qualified professionals have anonymously peer
reviewedthispublicationfortechnicalaccuracy.The
ANR Associate Editor for Urban Pest Management
managed this review process.
To simplify information, trade names of products
have been used. No endorsement of named products
is intended, nor is criticism implied of similar products
that are not mentioned.
This material is partially based upon work
supportedbytheExtensionService,U.S.Department
of Agriculture, under special project Section 3(d),
Integrated Pest Management.
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