<Does nature follow IPM principles? In other words, do plants that produce
toxic nicotine make it only if insects start feed on their tissues?
Or do they produce it continually for 24/7 protection?>

I am sorry, but this whole thread is daft. There are some things that have to be prevented, some require intervention, some can be let go. 

For example, you don't wait till the bear wipes out your yard before putting up a bear fence. Maybe you can take a wait and see approach with mites. I did that and lost my bees again. The ants, on the other hand, don't bother much so I am not going to put out poison.

In Nature's case, evolution has produced plants with poison, spines, tough bark, you name it. Animals have camouflage coats, evasive tactics, venom, etc. For survivability, nothing works as good as prevention. 

However, some things are more costly than they are worth. If a plant or animal spends too much energy in preventing things, they may have not resources for other things, like reproducing. 

You can find examples of anything you want in the real world. For every example, there are plenty of counter examples. I wouldn't make too much out of what Nature does or does not do. 

Pete

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