Hi Kitty-lover! Really after those Japanese Beetles aren't you?!?
I have seen a homemade Japanese Beetle Trap, but cannot state it's success, as I have never used it. You start by cutting the neck off a one gallon plastic jug, and fill it 1/3 full with a fermenting mixture of water, sugar, crushed fruit, and yeast (like a mush).
Strain out the beetles when trapped and dispose of them, and reuse the mixture.
You should probably use several of these, and also consider planting plants that Japanese Beetles are attracted to away from where they are attacking, with the traps near that attracting plant. An example of a plant that Japanese Beetles are attracted to is Borage.
Remember though, that this is only eliminating the beetle, and not the larvae, that live and feed on the roots of your grass.
I hope this helps, and you conquer the beast!!
Let us know how it works out.