Put down a season long grub control if you are OK being non-organic.
You can stop the fall part of their life cycle.

http://ohioline.osu.edu/hyg-fact/2000/2504.html

If you are organic use Milky Spore, but is does not do much unless your
neighbors apply it too.

Jim

CB wrote:
I'm noticing a ton of dead japanese beetles on my lawn, particularly under
my kwanzaan cherry trees. I've had a rough time with getting grass to grow
on my lawn due to grubs and the like. I wonder if these dead beetles will
pose a problem for the future lawn? Any ideas?