Jangchub wrote in
:

Bt of any variety will have no effect on beetle grubs, but milky
spore will.

http://www.pueblo.gsa.gov/cic_text/housing/japanese-
beetle/jbeetle.html

or: http://tinyurl.com/auphq

halfway down the page, under biological controls.

Bacillus thuringiensis (Bt)--Bt is a naturally occurring soil
bacterium typically used as a microbial insecticide. The Bt strain
registered for the Japanese beetle is for use on the grub stage
only. Bt is a stomach poison and must be ingested to be effective.
Apply it to the soil as you would insecticides. Effectiveness is
similar to that of insecticides. Check with your extension agent
regarding the availability of Bt.

it also suggests nematodes & parasites, as well as habitat
manipulation.
HTH
lee