By the way, as you know these are not the pesky root knot nematodes that afflicts Florida soils. If you just talk about nematodes down there, keep in mind that you are talking about one kind and EVERYONE else is talking about the other.

The beneficial nematodes work by carrying a disease to the grubs. Nematodes enter the grub by whatever orifice they can find. As they enter the grub, the disease they carry is wiped off onto the grub. The grub is almost immediately paralyzed and dies in less than 48 hours. The nematode lays about 250,000 eggs which hatch in a few days. Then they feed on the diseased grub and, if the soil is moist enough, crawl away looking for more hosts.

I am going to order a BN combo, steinernema feltiae and the Heterorhabditis bacteriophora which is the type that is better for the grubs. The other type works on leafminers, fleas, cutworms etc.

I am going to try sort of like a worm bin so I can cultivate many generations of Beneficial Nematodes so I can always have them on hand, considering they are so expensive when you order a single batch of a millon or 5 million of them. I finally found a site that mentioned someone doing this, using a Rubbermaid type container (20 gallons) filling it with 1/3 of moist compost, and then buying mealworms, silkworms, and crickets and then unleashing the beneficial nematodes. The worms died quickly like 2-3 days and same with the crickets. In 10 days or so the dead insects were crawling with new baby nematodes. Then some can be used in the yard, while the rest can stay and start the process all over again with fresh mealworms and crickets. I'm guessing the mealworms and crckets are a lot less expensive than having to order the BNs 2-3 times a year, especially when you factor in 2 day air delivery, which isn;t cheap.

My question is will beneficial nematodes attack grubs in this stage or are these too developed?
Yes the nematodes will attack grubs in all stages. And the dead ones will make more nematodes.

Just wondering if this is still the very larval stage that nematodes attack?
A grub is the larva stage.

I'm thinking of ordering the Guardian/Lawn Patrol combo.
Miky Spore can take 3 years to really get going. Also it ONLY kills the Japanese Beetle Grub.

The lawn is obviously swarmed with grubs from the yellow spots from them eating the roots and killing patches of grass, and also the amount of holes and also the Raccoon and mole activity during the evening.
You need to actually scoop some grass up and really see what you have.

I did apply Milky Spore last spring and also just again last week to see if this would help. No immediate results, so I'd like to unleash the beneficial nematodes to clean up the rest of the grubs still present and to build up a super colony of the beneficial nematodes hopefully to survive until spring and then really go to town and build up an army.
As stated before it can take up to 3 years to really get going.
To speed up the process you would need to be patient.
I mentioned dylux because it works immediately and lasts for 1 day only.
I sell Milky Spore and if you were buying it from me I would want you to be satisfied.

Not sure waiting 3 years is a smart strategy especially if even by your own words Milky Spore only kills Japanese Beetle larvae. If the grubs I have were say Chafer Beetle larvae (and maybe they are?) I'd be throwing money away, as well as waiting 3 years to finally have a decent yard.

Weird thing is the front lawn is a mix of grasses /weeds and there are no regular watering going on and I see no grub activity or moles/racccoons/voles etc. Almost seems like the more care you give your lawn the more problems happen initially until the grubs are under control.

Before I saw the lack of results from the first batch, I bought 2 other varieties from buglogical.com (Heterohabditis and the Steinernema Carpocapsae). With the 3 different strains of Beneficial Nematodes I was expecting joy but several weeks later I still see no difference. With these 3 varieties I should not still see ant mounds or slugs or the grubs. By the way I ordered 50 million of the last 2 varieties in which they claim 50 million would cover a half acre. The area I treated was less than 1/10 of an acre, heck probably 200 square feet. Using 2 of the 50 million batches is would effectively cover a whole acre and I still don't see results in a small 200 sq foot area which tells me these things weren't alive. I also started 2 other containers with compost and added 2 different strains in each container and added mealworms and grubs and they werent dead within 2 or 3 days and are still alive today over 2 weeks later, again telling me the beneficial nematodes were not alive. So to make a long story short $200 spent and no results. Very disappointed.

Did you water the ground real well after you applied them?