Upon hatching, caterpillars feed in groups on lower leaf surfaces and skeletonize the leaves. 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 defoliates entire trees.
A number of parasitic wasps (tiny and stingless), including Cotesia (Apanteles) species and Hyposoterfugitivus, 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 insects 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 caterpillar's natural enemies. Bacillus thuringiensis—which is sold as a variety of products including Safer Brand Caterpillar Killer or Greenlight BT Worm Killer—is an effective spray for redhumped caterpillar control. Bt, as it is commonly known, is a bacterial preparation that causes a disease-like condition in many types of caterpillars. They stop eating several hours after feeding on a sprayed leaf and die a couple of days later.