Tithonia is a favorite of Gulf Fritillaries
Not only a favorite of Gulf Frits, dark Swallowtails swarm Tithonia, too.
These Tithonia plants self-seeded from last year's plants. They form a bed about 6 x 10 feet, backed by Duranta and Crape Myrtle.
In a drought Tithonia plants sometimes shed some leaves and look a little shabby, but the flowers keep coming, especially with a little deadheading.
Here's an interesting link to information about using Tithonia as green manure and instructions for propagating plants.
Pentas are still my summer favorite and that of Spicebush and Pipevine Swallowtails but the Tithonia bed stays busy any time the sun is out. Remember that maintaining continuous nectar sources for a variety of butterflies requires a diversity of plants.