Answer: Without seeing it, I'm not sure what you are dealing with. However, caterpillars sometimes attack crape myrtles. These are the larvae of Pyralid moth and the caterpillars are approximately 1 inch long when full grown. Eggs are laid in masses and young larvae produce webs and feed in groups. As larvae mature, they spread throughout the plant. Most commonly found on Sophora secundiflora, Texas Mountain Laurel, but also found on crape myrtle, and honeysuckle.
The larva does the damage as it feeds on the young, tender leaves of new growth as well as occasionally on the older leaves and stems of the plant. This feeding damage can be small tracks and pin-holes caused by the tiny, newly hatched worms, as well as feeding damage on the edges of the leaves from larger, more mature worms. Additionally you will sometimes see leaf curl where the feeding has scarred young leaves, and caused them to grow misshapen. Even these damaged leaves are benefiting the tree by continuing to photosynthesize and produce food for the growing tree. Once the tree has enough healthy growth, it will often drop the damaged leaves.
No management may be required on mature plants as the worms rarely consume enough foliage to damage the plant. However, young and/or newly installed plants with a small canopy may need to be protected with a product called Bt (sold as Dipel or Thuricide). Bt is a bacterium that acts as a stomach poison so the sprayed leaves must be consumed by the caterpillars in order to provide control.
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