I had to look it up to find out what tibouchina was, never having grown it myself or seen it in a nursery.

Judging by the structure of the flowers as shown in internet pictures, it doesn't look like it'd very popular with butterflies. Butterflies usually like flowers with obvious access to the nectar, either through little 'portals' like lantana and butterfly bush or trumpet-shaped flowers, which hummingbirds also like. I don't see this on tibouchina flowers. I could be wrong, though - sometimes they use flowers you wouldn't expect.

Sherry

I am not sure as to their butterfly attracting attributes, but it is certainly one of my fave flowers. Very cold sensitive though, Don't leave the fridge door open too long LOL

University of Florida's rating for nectar : "Some nectar value"

In practice that would mean that butterflies might
tolerate some begrudgingly when no good stuff is available.