Question
Hey, Jack. I read your response to the other reader. I have two types of crape myrtle: pink Miami and red Dynamite. Both have the black powdery substance on the leaves and I did find aphids as you suggested to another reader. However, I have two other bugs in great quantities: a black insect, less than 0.5 inch long, with black spikes and two rows of orange spikes on it's back midsection and a round orange bug, 0.25 inch round, that looks like a larvae with couple of black spots on it.

Answer
Cathy,

The black powdery substance is mold that is growing on the aphid honeydew. Aphids excrete this sweet honeydew to get rid of excess sugar that they extract from the plant, and fungi (mold) love it. You can remove both the aphids and honeydew with insecticidal soap. Here's a link to using soaps for aphids and spider mites http://www.livingwithbugs.com/insecticidal_soap.html that may be useful.

The other insects are related. The one with spikes is the larva of a ladybird beetle (ladybug) and the orange one with black spots may be the adult (I'd need a picture to be sure). These prey on the aphids.

You might want to google "ladybug larvae" and compare pictures.

Post a follow up if this seems not to match.

Jack DeAngelis, PhD
Extension Entomologist (ret.)
My website about home and garden pests: http://www.livingwithbugs.com