There are lots of grubs that are harmless, so unless you're actually seeing damage that can be attributed to grubs, leave them alone. The white ones with the brown head, for example, are probably Junebug grubs, and don't do much damage as far as I can tell. There are others that are a problem, so hold onto a few and take photos to use for identification.
Take a look at some of the turf care tips that are scattered throughout the site. In particular, the Lawn Care Forum run by David Hall
. He comes through regularly and answers several questions at a time, so if you post there you'll get an answer eventually, but do yourself a favor and scroll through several of the pages of questions already raised and you may find something that works for you. Meanwhile, putting out beneficial nematodes will help with some of the pests in the garden and the turf like cut worms and other caterpillar and grub types. (I don't know if they control the Junebug larvae). On those bare spots you may be seeing the result of compacted soil or the result of years of chemical fertilizer use, etc. Aerating, spreading a thin layer of compost, broadcasting dry molasses or corn gluten meal, sprinkling rock powders, there are lots of things that may help that lawn that have nothing to do with fighting grubs.
The point of organic gardening is not to remove every pest that is out there, but to keep them under control with beneficial insects, biological treatments, and organic products. Good luck with the Bermuda - the worst weed in the world (in my humble opinion!)