Nematodes can work, but they can be pretty tricky. The conditions have to be just right when you apply, the shipping and storage needs to be have been done properly, and so there are a lot of failures with nematodes. If you're not fussy about whether it's a natural control or not, just use Grub Ex or any similar product with the active ingredient "imidacloprid" (it's on the label). It's very effective. One application in spring should be effective for 3 months or so. In your warm location, the long (year-round?) season might require a couple of applications a year. You might check with a local garden center to see what they say about that part. Be sure you follow label instructions.