Thank you for your reply.
I should have noted that while I moved most of my plants to semi-hydro, I still have some orchids in bark or sphagnum moss, as well as several orchids on cork or fern mounts.
It is certainly possible that I did not thoroughly clean some of the organic materials from the roots when moving to semi-hydro as well.
Can you please recommend a good broad-spectrum insecticide that will work?
I note that while I have used a Physan solution to spray on some of the leaves, I have not treated any of my semi-hydro pots with insecticide before, so would like to learn what insecticides are good both for preventative care and maintenance.
I have just ordered some more Prime Agra so I can move more of my orchids over to semi-hydro.