said by Voxxjin:
After the garage door was installed and I screened off the 'windows' I have very few bugs in there.
The trick I mentionned is only to "repair" the damage done.
As in, if you do get a lot of bugs in your garage and you want to get them out, leave the window open until the morning. Most of the bugs will have left the garage. It's not a solution to preventing the bugs from getting in.
As Cowboyro said, having no lights in the garage is best.
Lamp posts near the garage door, outside, will give enough light to see in the garage, but the bugs will stay near the lamp posts.