The grubs you have now will do no or very little damage to yoyur turf. They are last years grubs, and have resurfaced and will begin pupating soon. They virtually stop feeding, and feed very little (if any) at this time of year. You can waste your money and traet them, but it won't help you as you will have new ones in late July and august again. The best way to treat them, would be to use Merit. Apply this in June, when the June bugs become active, breed, and lay their eggs. Then, a few weeks later, as the product is leached into the soil, it will be there active and waiting for the new laid eggs to hatch. As these eggs hatch, the new grubs will be instantly killed. (It takes much less product to kill an infant than it does an adult).
You can also just traet them with a product such as Dialox, but the residual effect is not as long. If you just have spots now, that's probably all you'll have in the future. I would just scout for new damage, and treat accordingly. I just don't like to blanket the whole yard, because it kills to many predators as well.
Grubs are no concern in the spring, and they are mature enough to mostly survive any treatments.
They are a warning of possible future problems in the early fall. ID the critters from their raster pattern, and you will have an idea if you need a preventative this summer. Jap beetles live as adults for several weeks, and can disperse away from birth site, so if they are the grubs, you can't count on them coming back. Masked chafers, on the other hand, do not feed as adults - their only function as adults is to mate and lay eggs. So if they are masked chafer grubs, it's likely they will reinfest the same area.
I really should not take credit for re-naming that forum. However one of the above posters send that to me in an E-mail. I have enjoyed laughing about their re-naming that forum and though I might share it at the right time.