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How to Manage PestsPests in Gardens and Landscapes
The redhumped caterpillar, Schizura concinna, is found throughout much of California. Though the climate of the coastal regions usually does not favor development of destructive populations, it may be a serious problem in the warm Central Valley. Trees most commonly attacked are liquidambar (sweet gum), walnut, and plum, although it is also found on almond, apple, apricot, birch, cottonwood, cherry, pear, prune, redbud, willow, and others. DESCRIPTIONThe redhumped caterpillar has four stages of development: egg, larva (or caterpillar), pupa, and adult (or moth). Eggs are laid in groups of 25 to 100 on the undersides of younger leaves. They are nearly spherical and pearly white. Caterpillars are 1 to 1 1/2 inches long when fully grown and have a base color of yellow. The body is marked with longitudinal white, reddish brown, or sometimes black stripes. The head is usually orange or brick red, as is the fourth body segment, which is distinctly humped and has two prominent black tubercles or spines. Each body segment also has less-distinctive black tubercles. Caterpillars rest with the hind end elevated. The pupa is reddish brown, a little over 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 have a wing span of 1 to 1 3/8 inches. The forewings are reddish to grayish brown and are often darkest along the hind margin. The hindwings are off-white to light gray or brown. DAMAGEUpon hatching, caterpillars feed in groups on lower leaf surfaces and skeletonize the leaves. As the larvae become larger, individuals tend to disperse and consume the entire leaf, leaving only the tough woody veins. When infestation is light, leaves on only a few branches are eaten, but occasionally a heavy infestation develops and entire trees over a large area are defoliated. Most severe defoliation occurs in summer. Even if completely defoliated, trees that are otherwise healthy can be expected to recover. When defoliation occurs on walnuts, the nuts are subject to sunburning. LIFE HISTORYIn autumn, caterpillars drop to the ground and spin silken cocoons. They remain inside the cocoons during winter and transform into pupae in spring. Moths begin emerging from pupae in April and May. They mate, and each female may lay over 200 eggs. The eggs hatch into tiny caterpillars that feed, grow, and finally 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. CONTROLA number of parasitic wasps, including Apanteles species and Hyposoter fugitivus, use the redhumped caterpillar as a host and on occasion provide an effective natural control. However, in some instances additional control measures are necessary. The simplest of these is to cut off the foliage that contains caterpillars while the insects are still young and gregarious. At this stage only small branches need to be pruned off to destroy a large group of caterpillars. The foliage can then be burned or the caterpillars crushed. Bacillus thuringiensis (sold as a variety of products, including Dipel and Thuricide) 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 Bacillus thuringiensis after the first skeletonized leaves have appeared. A forceful spray throughout the entire tree is needed for effective control. Bt will not harm the natural enemies of redhumped caterpillars and other insects like the more toxic, broad-spectrum insecticides do. Experience has shown that sprays for redhumped caterpillar control are often applied too late. Unless the caterpillars are present on trees, it is best to delay spraying until the next generation appears and is feeding on the leaves. WARNING ON THE USE OF CHEMICALS COMPILED FROMMoore, W. S., and C. S. Koehler. 1981. Redhumped Caterpillar--A Pest of Many Trees. Oakland: Univ. Calif. Div. Agric. Nat. Res. Leaflet 21064. SUGGESTED READINGDreistadt, S. H., J. K. Clark, and M. L. Flint. 1994. Pests of Landscape Trees and Shrubs: An Integrated Pest Management Guide. Oakland: Univ. Calif. Div. 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. Div. Agric. Nat. Res. Publ. 3332. PUBLICATION INFORMATION![[UC Peer Reviewed]](/IMAGES/logo-ucpeerreviewed.jpg){kind=logo}
Pest Notes: Redhumped
Caterpillar Contributors: R. E. Rice, Entomology, UC Davis; and R. Van Steenwyk, Insect
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