There are lot of sprays that will kill Japanese Beetles Sevin, and Eight are sprays that you can use that remain on the leaves and kill the beetles when they eat it.  They are washed off by rain so  need to be reapplied occasionally.  There are also contact killers  that will kill them on contact at the time you spray. Here are some links to products used for killing Japanese Beetle.

http://www.bonide.com/products/product.php?category_id=195

http://www.bonide.com/products/category.php?category_id=3&page=1&per=all

http://www.bonide.com/products/product.php?category_id=442

http://www.bonide.com/products/product.php?category_id=196

http://www.bonide.com/products/product.php?category_id=026