They are not necessary for proper blooming and do not spread botrytis blight.
Japanese beetles feed on the late blooms or the leaves.
Rose chafer is often mistaken for Japanese beetle. These light tan beetles with spindly legs eat the flowers. Rose chafers are killed by sprays but a reduction in the population may not be noticeable. This information is for educational purposes only. References to commercial products or trade names does not imply endorsement by MSU Extension or bias against those not mentioned.