to save seed from corn you need at least 200 plants to get a good sample size to keep the genetic dervisity up as corn is very likely to degrade over each session .

the cobs that you want to go to seed will be the best looking healthy plants have stright lines of corn with very little twists.

200 plants is the accepted minimum number of plants for seed saving, if the goal is to reproduce an exact copy of the parent corn and if no seeds from other sources will be grown with the seed you produce.

IS your goal to grow the SAME corn again, without bringing in seed from another source? If your goal is to improve the variety, you need ideas like saving seed from any plant that shows clever new traits (maybe least bug damage), and saving from plants that are thriving. These seeds should make up the majority of what you save. If you're not sure that you've saved seed from enough individual plants to avoid inbreeding depression, add in seeds grown elsewhere. They can be the same variety, or another that you think would complement your variety.

Know that EanG's advice will yield Bantam corn like what you've purchased, year after year. My advice will yield a more variable corn, with differences between one plant and another, and between one year's crop and another. Neither of those options is inherantly bad, but you need to consider which is a better match for your goals.

A middle road between the two would be to save money on seed and adapt the Bantam to your garden (without having to grow 200 plants) by saving lots of seed from your healthiest plants, and planting them with a few purchased seeds each season. You'd still be preventing inbreeding depression because the seed come from many plants, they just weren't all in YOUR garden.

I'm sorry, I just re-read your post and realized I allowed myself to get side-tracked.

I've used chemicals mostly for pest control, but am learning to be more organic. I've heard of an organic product called neem oil that might work for you. I know most bugs won't stick around if you spray with water that's had tobacco soaked in it. (This is harmful to a few plants, so google first.) Jalepeño peppers can be brewed into insecticide. (Harmful to plants if brewed too strong.) The compound that makes rhubarb leaves poisonous can be made into an insecticide. The tobacco spray is the only one I've tried personally. It worked well. May need reapplication after rain. (They all might.) I'd think twice before using these methods on ears I intended to eat. At least wash thoroughly. (Just like you would with sevin dust.)

Covering the ears with some kind of barrier would work too, IF pollination is already complete (or you're willing to hand pollinate) AND the bugs are not already in the ears.

That said, I would save the seed of the least bug damaged ears by itself. I'd either plant only it, or make it a large part of my planting. Tighter, thicker husks make entry more difficult, but not impossible. Selecting for that should reduce bug issues in the future.