Gritty mix will not keep mealy bugs away. I made the mistake of buying a small variegated jade from a big box store, and realized a few weeks later that I had introduced mealies to my collection of cacti and succulents at the office, all of which were growing nicely in gritty mix. I brought them under control with systemic imidicloprid. I don't use that outdoors because it kills bees. An organic method of controlling a light mealy bug attack is to clean them off with a Q-tip soaked in alcohol and then to spread used coffee grounds on the surface of the potting mix.

Others can address your questions about screening. I use insect screen to screen turface and don't lose much of it.

Insect screens are usually less than 1/16 inch openings. Using a 1/8 inch you will lose too much of your Turface. The reason for screening is to get out the fine dust like material. Al

One + of using soils that promote healthy root systems is the fact that healthier plants are better able to resist insect and disease, but there is no guarantee that a healthy plant will be immune to insect/disease predation.

I too, use a spray from Bayer with imidacloprid in it for most insect infestations other than mites (has to be sprayed outdoors). I also use a soil drench with imidacloprid, but the spray works better. I don't like the granular vehicles that carry imidacloprid (Merit/Marathon/Dragon) because they filter down into the soil, and I've repeatedly seen evidence of weakened root systems whenever I've used it.

I too, use aluminum insect screen to remove the fines from Turface, grit, and the prescreened fir bark (1/8-1/4) I use.

Al

I use either a spray or a systemic as a means of prevention. Bugs will still be attracted to the plants, but there's less chance of harm or mass infestation because of the more inorganic environment, and the better health of the roots, thereby the plants, themselves. Even so, an ounce of prevention is worth a pound of cure.