Best way is to squish them I'm afraid!

I just saw this question from the main screen Meanie and came to it to give an answer with my usual subtle approach. That is 'with a ruddy great hammer.' I suppose a gentle squish has a similar effect though. Lol.

My one remaining Regal Lily comes up bravely every year from deep beneath the ground and eventually is wrecked by these wretched beatles. At the moment it is looking very whole. My method is a quick grab. Onto the path and a hard stamp. Beware that they let go and tumble through the leaf axils and just vanish from view.

Also helps to know what the grubs look like and to remove them too. Bird droppings on the underside of a leaf, remove the leaf and stamp!

A latex glove, a pair of spectacles (in my case) and rigorous examination of the plant at least once a day. Stealthily pick the beetle up and crush between finger and thumb...

their eggs are orangy red and easy to see on the underside of the leaves. crsh them between finger and thumb.

They have also developed the knack of landing red side down so watch where they fall

I'm squeamish about squashing with finger and thumb so I shake the beetles into a white yougurt pot, then tip out and stamp quickly. If they drop to the ground they become invisible! I remove the disgusting 'bird-dropping' larvae by wiping the affected leaves with damp kitchen paper.