I have noticed some flies on mine as well. I don't see where they are hurting them but I just find flies annoying in general lol.

My only suggestion may be if your soil or grass stays wet gnats seem to really like the wet damp soil, especially in pots. The flies are most likely not interested in plumeria & may be close by due to weather or something else.

When a fly's bugging me it gets a shot of hair spray. The wings stick, the fly falls and that's that. I actually keep a can of cheap hair spray on my outdoor table.

I know a plumie person who hangs the sticky fly traps around her yard and it seems to do the job catching gnats, Flies, and other bugs. If you have an abundance of flies try it as it does work.

Good luck