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Interesting post, thank you. I do have a few questions though.

AFIK, there is no such thing as a biocontrol that destroys its host. It can reduce an infestation, but will help only if the trees are capable of fighting back. Given the usual USFS ridiculous stand density, it is unlikely that these trees are in very good condition. Is that the case in this instance?

I didn't note from the article, but are these Afghan pine beetles? If they are, they should be eradicated if possible, not merely treated.

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?

Finally, one would need an enormous count of these worms to do serious damage to an advanced infestation (which, because of the bureaucratic delay inherent to government forest management, this probably is), isn't what you are describing more appropriate to preventative and early treatment rather than an advanced case?

Thanks.

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.