I've had an irritating day, but you made me smile with the idea of your force feeding the grubs!

"Take it! Take it!"
"NO!"
"I said TAKE IT! THERE! Now swallow it!"
"NO-pfff..." (gagging sounds)
"Stop spitting it out!"

I came across an article from 1995 about Japanese Beetles in Iowa, they said it didn't work very well (below). I remember something about a big bad batch of milky spore, but don't remember when it was. If you have it, I'd sure try it.

Sue

Here is a link that might be useful: Japanese Beetles in Iowa

Digging up and then rolling some grubs in some Milky Spore Disease might be one way to be sure they make contact with it but not a sure way to get the spores inside them where they need to be to become active, kill the wee bugger, and then become dormant and invade your soil some more.
Milky Spore Disease, Bacillus popilleae, is a disease specific to certain beetle larva and the bacterium is dormant, spores, that will become active again in the gut, digestive tract, of these larva (there needs to be a fairly specific type of gastric acids to do that) where the, now alive, bacteria eat the larva from the inside out and when the lava die the bacteria once again go dormant and wait in your soil for more grubs to ingest them.
Where there are reports that Milky Spore Disease does not work well is where people have expectations unwarrented, where people expect this product to immediately start killing off these larva just as the poisons they prefer would.

The annoying thing is there is so much Info - Positive and Negative concerning Milky Spore, out there. The Official site has FAQ, but no Replies to anyones questions. I am going to try it, knowing its going to take several years before I see results. I will add it in the spring and fall next year as well. In the mean time i will keep pulling them off and in a bucket of water. I am trying to stop using chemicals totally, but I will have to use some Seven on my small bushes and trees, that are not established. If I didnt have to go to work i could guard the plants 24-7...AHHH Retirement....some day, Sigh.