Your thread got hijacked into irrelevant discussion about merits of NAPA in soil that is no help in dealing with the Thrips youre showing in your photos!!
Only the adults can fly so what youve photographed are probably the early larval forms. Your neighbouring trees in gardens or woodlands could be a source of regular re-infestation so routine treatment of the affected bonsai with insecticidal soap seems a good plan. Which bonsai are affected?
Thanks! Yeah, I noticed that the landscape tree right in front of the trees of mine that are affected exhibit damage that is similiar to what I'm seeing on my trees. I looked up the tree using a plant/tree identifier app on a smartphone. It came back as Lophostemon confertus (know as brush box, Queensland box, Brisbane box, pink box, box scrub, and vinegartree according to Wikipedia). I haven't actually seen the same bugs on this tree though but I also haven't looked too closely. Also nearby is a eucalyptus tree, I think -- I couldn't get close enough to its high branches to get a good picture for the app.
So far, the bugs are all over three of the giant sequoias (Sequoiadendron giganteum) that I have and my Monterey cypress (Cupressus macrocarpa) but it is not on any of my other trees, which are all decidious, with the exception of a Cryptomeria.