Build the growing cylinder with wood post or with 4" pvc post.
Attach circular plywood plates at top and bottom.
(Optional: Cut half of the bottom out of a plastic pot and slide it down over the post, so that it sits on the bottom plywood circle. Put a few rocks in the pot to hold it down.)
Wrap insect screen around the plywood top and bottom plates and affix with staple gun and hot glue, so that a screen cylinder is made.
Cut a square hole out for a door, and cover with a square of screen that is 3" larger than the hole.
Use velcro or hot glue to attach flap, and you have a doorway to take plants in and out.
You can make several doors to access different parts of the cylinder interior. If you use the plastic pot at the bottom with rocks holding it down, then you can glue the screen to the outside of the pot. Then you will be able to lift the pot up and the screen with it, when you want to change plants or gather larvae or pupae.