Those things did a number on my canna last summer too. The only thing I found that worked is picking them off by hand, putting them in a jar, and feeding them to my koi. I was out there every morning and evening cleaning the plants. I wasn't able to get rid of all of them but I did notice reduced numbers.

If anyone has a better remedy I'm also interested.

I have never tried this and I am trying to find someone who has, but a organic remedy might be a beneficial nematode that kills the larvae stage of this beetle. it kills grubs of the of all kinds of insects including Ants and Termites without attaching earthworms. I do not know whether I believe all this hype, sounds too good to be true. It is watered into lawn and garden soil. These microscopic worms then attach the grub of insects. I think the name is Steinernema something. There are different types for different conditions. The only problem is that it won't kill the bugs that come from your neighbors yard but maybe it can reduce the numbers. I believe these worms have to be reapplied every year in early spring. Anyone know about these?

A follow-up.
My Manzano survived the small attack by those beetles and is now producing bunches of fruit. Can't wait until they ripen. Lots of water and lots of fertilizer.