If you have thrips then the leaves will have a silverish or grey hue to them when viewed from the top; this is because the thrips strip the tissue leaving no green pigment in the tiny holes.
For most soft bodied insects you can treat your plant with a spray solution formulated from water and a tiny amount of dish soap; this only kills the insects and not the eggs so you need to re-spray again once the eggs are hatched.
I believe that for thrips the eggs take two weeks to hatch so repeat again in two weeks, and for spider mite it's three days.
You will need to wash the spray off the plants almost immediately with clear water, don't spray while the plants are in direct sunlight and use a decent sprayer like the pump up ones with a lance and spray both top and under the leaves the stems and the top surface of the soil.
If you can't identify what insect is eating your plants then it is better to assume the worst which are spider mite; for spider mite you need to spray every three days for two weeks (five spray sessions)
When ever I suspect insect attack I first take a sample from a leaf, I use parcel tape and carefully stick it to the underside of the leaf, then I carefully peel it back off starting at the stem end while keeping some lateral tension in the tape, then with a powerful lens or small microscope I inspect all the dots I see on the tape.
Once you know what you're dealing with it gives you the confidence that you can control the situation, you just need to exploit the week part of the life cycle.
If on the other hand you're having trouble with flying insects then simply keeping your plants under nets will keep flying insect away. It is also worth examining other plants in your garden to make sure your bug infestation isn't being picked up from somewhere nearby, you would do well to treat these plants also to reduce the threat.
Some insects make their way to your plants by crawling on the ground, you can reduce this by putting rhubarb leaves on the ground, the rhubarb leaves contain oxalic acid which is toxic to insect and also toxic to animals and people if ingested, so only do this if you don't have pets or children in that area which you shouldn't anyway.
One last thing, if you're growing in a greenhouse then I would recommend getting yourself a sulfur burner (vaporizer) which not only keeps molds from forming but it is good for keeping pests away too, remember to read the instructions properly and ask in the shop how to use it, sulfur can be toxic also if it becomes a compound.
I have used a sulfur burner to great effect and managed to completely save my flowering plants from a serious spider mite attack
I hope some of this info may be of help, and good luck.
