I'm not familiar with Harlequin Bugs. Are they eating the petals or the leaves?
Banana Cream looks beautiful in the catalogs. I love that color of soft yellow. I have a white one called Becky but it's not blooming yet. When it does, I'll watch to see if anything starts munching on it.

Here is a link that might be useful: Google Images - Harlequin Bug

I have had them before, but they seem to be selective in the plants they attack here. I think mine was on a radish plant that I had let flower. At that time they weren't bothering anything else. They are a stink bug and I hate stink bugs. I don't have a solution or tip. I would spray your choice plants and not the whole garden.

Here is a link that might be useful: harlequin bug

Hi,
The have actually killed one plant now, it was called an Obsession plant and it's near my daisies. They appear to suck the moisture out of the stems. Though I saw the bugs hiding in the 'leaf joints', around the soil at the base, and sometimes on the leaves - the plants stems collapse, turn brown and die.
I believe they are a type of harlequin bug, but I will try and capture alive some for a better identification.
Mel

I think you have established that they are not beneficial so I would spray with something. Sometimes you can spray in the evening to try to avoid bees. I hate poisons and try to handpick etc. I have not had any luck with mild methods on any stink bug relatives. Last year I spent lots on a trap that didn't work. I wasted lots of time hand picking them and throwing them in soapy water. To me a harlequin bug is just a decorated stink bug. The problem is the spray may not kill them. The babies look like adults but don't have a tough shell yet. Maybe yours are babies.