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Thanks to all for responding. To be clear about my expertise, I am a gardener, not an entomologist not a forester.

I used predatory nematodes ("PN") in my garden, my lawns and on my pine trees. The white grubs were almost eliminated from the garden. (Visual census comparing the first year tilling with the 2nd and 3rd year tilling.) I don't currently have problems with lawn grubs. This area has problems with pine borers so I sprayed as a preventative. The trees look better than they have in years but I can't tell you with certainty that they were suffering from an infestation to begin with. I do note that the sites linked to above specifically list pine borers as a controlled pest

"Given the usual USFS ridiculous stand density, it is unlikely that these trees are in very good condition...
Thinning the forest can reduce the water competition that seriously degrades the sap flow that the tree uses to defend itself from beetle attack. I note you didn't mention that. Why not? Wouldn't a selective thinning, removal of infested trees, and low-temperature burn help the trees fight back?"

I would think that use of PN does not take the place of good forest management. Monoculture and crowding of stands of lumber or fields of vegetables favors insect and disease transmission. They should thin crowded stands. We should hang on to some old growth, but I don't have a problem raising trees for or using lumber. (From a carpenter's son, and former carpenter and cabinet maker.) Again, PN is a biological control, I doubt that either it or any chemical controls would be 100 percent effective. At some point a forest may be so badly damaged that it should be clear cut or burned.

"are these Afghan pine beetles"

Mountain pine beetles according to the article.

Re aerial application, oxidation, etc;

For gardens and lawns PN is supposed to be sprayed in low light, high moisture, and cooler temperature conditions. PN survive well in highly oxygenated water. You are instructed to water them into lawns after applications. Before I sprayed my pine trees I sprayed down the bark as high as I could reach while standing on a ladder. I cant provide specs on aerial application, but I would guess that cloudy conditions at the end of a rainy day would be the best conditions. This is probably something that forest management experts should discuss with the bio labs that raise PN.

"one would need an enormous count of these worms to do serious damage to an advanced infestation."

I suppose--not know--that since the nematodes are parasitizing the grubs that their numbers will increase to match the available food source. They may not do well in dry or extremely cold conditions, which could suppress their numbers.

Hopefully this, or some other control measure will be effective.

I am a gardener, not an entomologist not a forester.

It sounded like it (which is not a perjorative); I'm a sort of cross between the two.

"one would need an enormous count of these worms to do serious damage to an advanced infestation."

The point is that the beetles are propagating without nematodes while the nematodes can't propagate without beetles to eat. Mathematically that means they cannot eradicate but can only control a population.

I suppose--not know--that since the nematodes are parasitizing the grubs that their numbers will increase to match the available food source.

How effective this will be depends upon how far behind the curve one is when the nematodes are applied (breeding rate of nematodes v. beetles). It's a question of economics. I doubt that the nematodes are very good at moving large distances to find a new host without drying out or starving (which would of course, constitute nematode-cruelty; where's PETA when you need them? ;-), so, to be an effective control, one would need to cover the tree with only a few beetles in it to eat, which is an inefficient means of preventative control. If one waits until there are enough beetles to feed and propagate nematodes you are already behind the curve. IOW, it may work in your yard where you value highly each tree, but I question whether it is an economical control process on a landscape scale.

Good response, thank you. I value first-hand experience highly.

Interesting thread re: predatory nematodes.

It boils down to money. There are millions of acres of overstocked timberlands. We scarcely have the money to treat the trees in the campgrounds. (yes, I have seen men in bunny suits spray high value campground trees with a 60' boom truck)

At some point, we will have to take responsibility for the fact that we humans have interupted the natural cycle. We cannot "wish the overcrowded trees away" nor look for a silver bullet.

The fact is that there are too many trees - too many for the land to support. If the pine beatle doesn't kill them, drought or disease will.

I say it is better to turn these trees into power or products then to let them become worm food or burn in a confligration.