Unknown Pest Eating my Vinca Periwinkles
Hi, I am brand new to flower gardening and have just recently put up my first flowerbed. I planted several different types of flowers and most of them seem to be doing fine but in the past week I have noticed that something is taking quite large bites out of my Vinca periwinkle blooms. It looks at if something is taking a round cookie cutter to the blooms on the edges. If you look very closely the cuts are slightly serrated but they are even and symmetrical. I have no idea what could be doing this. I never see anything near my flowers, and I don't see any bugs on them except for an occasional ant. Whatever is doing this, prefers the periwinkle and they have choose to only eat the white and light pink blooms, yesterday, a bite was taken out of one of the hot pink ones though.
If anyone knows what could be doing this I would really appreciate some advice on how to get it to stop. It is destroying my blooms. I have uploaded a photo of the damage from my phone It's not the greatest photo but you can see the damage. Please HELP ME!!! Also, on the outside of the bed I have impatients but it doesn't bother those, even though it would pass them first to get into the bed.