What are these shallow markings on my chili leaves?

Question

I had some green aphids, and killed them with an acetamiprid based insecticide. Everything after that seemed fine until recently. Some whiteflies started showing and I treated those with a mixture of rubbing alcohol, liquid soap and water. After few days they seem to be gone for the most part. But now, some plants are showing different symptoms and I have no idea what's wrong with them. I get it, those eaten by the bloody flies have some issues, but what's happening to the others?

Here are some of them:

Some Cayenne plants seem to be fine. But some got this:

Here is a Jalapeño with some other problem:

To me, it looks like it's been eaten by something, but there were plants with more white flies on them and they practically have no damage. Also, some Royal Black chilies and one Jamaican Hot lost more or less of their leaves without having no other symptoms at all. I used some granulated NPK fertilizer (15:15:15) on a few plants and most of them didn't get any. This doesn't seem to matter, because there are some sick and some healthy in both groups (fertilized and not). I don't know, maybe I did bad with this solution against white flies, but I'm not so sure.. I mean, some of the plants are totally fine and some are very sick. Any ideas?

Update: 2015/06/07

Help people! This is starting to kill all my plants. There are no more white flies, they are just wilting. Here's my biggest Jalapeño, which was just fine until today.

What's this, how do I stop it?

Answer 1

This looks like Thrip damage. From the University of California's Integrated Pest Management program:

Thrips feeding on plants can damage fruit, leaves, and shoots and very noticeably affect plants’ cosmetic appearance. However, thrips rarely kill or threaten the survival of trees and shrubs. Herbaceous ornamentals, and certain vegetable crops, are more susceptible to serious injury from thrips feeding and thrips-vectored viruses, especially when plants are young.

Thrips are difficult to control. If management is necessary, use an integrated program that combines the use of good cultural practices, natural enemies, and the most selective or least-toxic insecticides that are effective in that situation.

Keep your plant healthy, and fertilize often, and the pests will likely move on. Treating for thrips is often not very efficacious, but thrips do tend to avoid healthy plants.