To confirm your plant has hoplia beetles, inspect a flower and you may also spot this culprit (or three) hiding inside. The beetles are small, brown, and their undersides look like they've been dusted in gold. If you hold one in your hand, they will “play dead” and not move so you can examine them.
The best way to manage hoplia beetles is regularly handpicking or shaking them off the flowers into a bucket of soapy water and then disposing of it. This can help reduce beetle populations in the future. You can also fill white, 5-gallon buckets with water and a few drops of detergent. The white color may attract the beetles which will fall into the bucket and drown. Luckily, their populations begin to dwindle by June. You can read more details about these methods in the UC IPM Pest Note: Hoplia Beetles.