I have replaced all of my screens with No-See-Um screening A finer mesh and it works well...'usually'.
As for a natural product...you want a glass sealer, a handful of fresh crushed up parsley and bottle of Apple Cider vinegar. Into the sealer with the parsley and cider and into the fridge overnight. I have a handy dandy little spray bottle that is pocket sized..spray all over the exposed areas. Yeah..you can smell it..till it dries...then no smell and works like a hot ****.
Gary Haupt