phoebe51:
Sorry to hear about your plight.
You can get good control of aphids with ladybugs.Lacewings
larvae will eat mites.FYI your praying mantis also eats
benefital insects as well as the bad guys.The whitefly
parasite(a parasitic wasp) will eat your whitefly.
I have not had problems this year with the insects
you have. Mine have been leafhoppers on all my salvias.
I get whitefly on my S. gauranitica I spray it with
Insecticial Soap w/Seaweed Extract. I have to do that daily being organic's are contact kill only.The predatory insects
usually do a better job being the insects don't build up a
resistance to being eaten.You should also have a small fan
blowing over your seedlings.The air movement helps keep
populations from getting started.The other thing is using
a yellow pest strip to monotor insect activity so you are ahead of the problem.
Art

Keep an eye out for ants, which will move honeydew producing pests like mealybugs and aphids around. You can use a fine jet of water to blast off the larger pests. They won't regrow their stylets once the water jet has removed them.

To reduce stress, try modifying the growing conditions. Perhaps there is an imbalance with the fertilizer nutrients, like too much nitrogen and too little phosphorus. There is an optimum ratio of heat to light to moisture to fertilizer for each species, and it can differ on the size of the plant.

I am getting lush growth on my plants this summer, and the recent buildup of pests is an indication that I need to thin out the foliage to allow more air circulation and open up the developing refugia for predatory insects.