USDA sent folks to Japan to find out why the beetles didn't go crazy there, and they discovered a bacteria that destroys the grubs in the ground stage, but since the beetle was introduced here, the bacteria (milky spore....so named because it turns the grubs a milky white when infected) didn't exist here....hence they went nuts with no natural control.
USDA rolled the stuff out....they got barrels of it in in the 70's here, and sold it at cost. It is supposed to be a one time treatment...the spore (which only affects these grubs) spreads in the soil as the grubs die. But if the beetles get in an area that was never treated, they are gonna spread like mad until the spore catches up with them.
The stuff isn't cheap, but it's the only long term control for them.