You should upload more pictures. Especially of the insects you have seen. But it looks and sounds like "thrips". The thrips "Frankliniella occidentalis" (also western flower thrips) for example is very common and has a brown body. It is about 1 mm big and causes damages like shown in your picture. Before you can treat the plant, you need to be sure of the causer! Please upload more pictures of the damaged leafs and try to shoot a picture of the insect.

Continuation:
Okay. I can´t recognize which insect is shown in this photo. Please look at https://en.wikipedia.org/wiki/Thrips There are some pictures of thrips. Especially the nymph stage you should find under the leafs close to the leaf vein. They are yellow. The adults looks different - some brown. And they are fast and try to hide. Thrips suck at palisade mesophyll which fill afterwards with air and white spots emerge.. Just looking at the fotos it looks truly like thrips damage. But please make sure you find the insects before you decide how to treat the plants! Thrips are very common but not easy to handle. But still there are some pesticides to apply. The agents "methiocarb" , "abamectin" and "spinosad" find already use in the horticulture business. The agent "cyantraniliprole" is very new and just in some countries available. For hobby or organic production is "rape-oil" an alternative. I hope I could help you. Please let me know what you finally decide to do.