gaiaso, your nom de plume suggests that you might be a follower of Dr. Lovelock.
If that is so, I am rather surprised at the manner in which you went after the tent caterpillars.

I wish to emphasize that the inference was all mine and I apologize, upfront, if I did you an injustice.

Are you saying that I harmed the tree? My intention was to kill the tent caterpillars before they devoured my tree's leaves, without harming the tree. I know, folks say rip it open and let the wasps have at them.... I'm just not that trusting and besides, I have an agenda. I want apples!

I'm wondering if I've stumbled on to a really good way to kill specific bugs without leaving a residue that harms beneficials. That's what really want to know. I've had marginal success with soap sprays. It doesn't seem quite deadly enough. But is the ammonia TOO deadly? Am I going to throw other elements out of whack? I rinsed the tree with water when I was satisfied that they were dead.

I've since read about using ammonia spray on other soft-bodied insects. Slugs get mentioned alot. I've seen aphids cited, also the young squash bugs (red stage).

Can someone offer me a reason NOT to try it on my garden? Does anyone have specific information on the effects and limitations on using the ammonia in soap and water spray? Does it effect pH? Build up in some weird insoluable molecule?

Many people think that the tentworm caterpillars eating a trees leaves will kill it but that does not happen. The tree simply leafs out again and goes on about its business.
Many people, in an effort the control these wee buggers, do things that are more harmful to the trees than the caterpillars would be, but understanding a bit about these wee buggers can help keep them, as well as the Gypsy Moth and any other leaf eater there is. The Eastern Tentworm Caterpillar female moth lays eggs in a mass on the branches of favorite trees typically 6 to 18 inches in from a branch tip. In the spring when the larva are getting ready to hatch what I have seen is these egg masses turn a light bronze color, but they can be seen from the time Ma makes that mass until long after the larva hatch out.
The first step in control would be a dormant oil spray. The second step in control is after the wee buggers hatch and before they get too big, although there does need to be leaves out, and that is a spray of Bacillus thuringiensis, - Kurstaki, a spray sold as Thuricide, Dipel, and several others. A last resort might be a pyrethrin based spray used with due care since it is a broad spectrum poison that will also kill beneficial insects.

I think that wishing to get rid of tent caterpillars on a fruit producing tree is pretty important to a good crop. The trees will put their energy resources into making new foliage, rather than building great apples.

I don't have an answer to your ammonia question, gaiaso. I know that it might be harmful to foliage if mixed too strongly, but don't know that spraying it on the bark is a problem. It's not something that I would do. I'm a bit loath to suggest elixirs made of products that don't have labeling instructions on them for the use I intend. ;-)

Anyway, I'd suggest that you get some Thuricide or other liquid Bt-K product from your local garden department and apply it so that you can get rid of any survivors.

Keep in mind that BTK is only effective against these leaf eating caterpillars for a fairly short time. Once they are somewhere around 4 weeks old they are too big for the disease is not effective.