If the grubs are huge, the size of a pinky finger, they're helping you breakdown the heavily mulched layer you applied. They don't damage live plant material.

That said, the adults -- large green clumbsy flyers -- feed on *over-ripe* tomatoes and tree fruits.

Those japanese beetles probably did lay their eggs in your nice soft new beds /..\

link is to gov't info on japanese beetles, which answers most of your questions, and has photos including one of the grub (larva).

I have found milky spore to be of the most help, but it does take a while to be effective (about 2 years). And you will probably always be fighting JBs since they will travel to get food. But there is a difference between spending fifteen minutes hand-picking the all critters in your garden and seeing more beetles than leaf (which is what happens when you don't try any controls).

Here is a link that might be useful: japanese beetles info +photos

Please read carefully. The .gov site (link in the above post) states in part:

"... During the feeding period, females intermittently leave plants, burrow about 3 inches into the ground--usually into turf--and lay a few eggs. ..."

Also
"... In early spring, the grubs return to the turf and continue to feed on roots until late spring, when they change into pupae...."

Beyond that, grubs are *next to impossible* to ID from a photo on the web, or even in a book. Particularly when info re size, and distribution of the hairs on its butt, are lacking.

We forum folks are long-distance guessers when it comes to IDing one of these confusing insects -- among them grubs.

In such instances, in order to obtain a confirmed ID, one may need to take a sample to a local expert, among these are a University Extension Office, a county or state agricultural commission/department/agency, and/or a large independent garden center or farm store.

Thanks for the advice and info, you guys are great! I really like that website's description of how biological controls work, eg:

"the female wasp digs into the soil, paralyzes a beetle grub by stinging, and then deposits an egg on the grub. When the egg hatches, the emerging wasp larva consumes the grub."

Go girl, chomp away! Now, that's my kind of wasp :) The BT and nematodes sounds promising too. I'll look into their availability here.

But it's a relief to know that I don't have to be out there spraying stuff just because I've got grubs. The plants all seems to be doing fine right now, but I'll start thinking about grub control for next year. Thanks very much everyone for your input!

A nagging question remains -- Are your particular grubs a kind that need to be controlled?

jean001, hmm, good question there. Those in my comfy mulched beds matches the description and pictures of the jap beetle grub. Assuming that's so, should I be alarmed?

The dot-gov web site explains the lifestyle and habits of Japanese beetles.

Their eggs are laid in turf. The grubs (youngsters ) eat the roots of turf. They're not interested in mulched beds.

I doubt you have any reason for concern. When you find them, stomp them, or cut them in half, or feed to birds, or something else. And have fun with your new garden bed!

One of my flower beds was doing poorly all summer with the same annnuals that have flourished in years past. The plants seemed to be barely hanging on and did not grow large like before. In October, I dug through the bed and found dozens of grruubs. I’m sure they were just eating away at the roots.