Could be a leaf cutter bee, it looks bad but they don't harm the plant. Not much you can do because they fly.

thanks for your answer

They're good bugs. they use the leaf pieces to make their nests. They eat bad rose bugs so I'm always happy to see those half circles. It's funny, they usually pick one bush to cut from and leave all the rest alone and every year it's a different bush!

ow.. so i dont need to worry?

No, there's no need to worry. They don't do much damage and the roses won't miss the pieces.