Paula, Sorry to hear about your bug problem. I have the same problem with Ladybugs. I still have difficulty locating the exact area they are coming in. I did replace my windows which help cut down. Unfortunately they will find the smallest hole and come in. I doubt the siding is the culprit, because they would have to get around the siding, sheathing, insulation and drywall. An area that could help as well is to insullate the pockets in your basement where the floor joists meet the concrete foundation, that could help. Check your windows and seal any openings. Other penetrations could be the bath and kitchen vents, those could easily have screens put over the outside. Another possibility would be your vent for your water heater, check that in the basement. Lastly check the attic skuttle hole to make sure they are not finding a way through the roof vents and into your attic and ultimatly in your house. These are areas that can help cut down on them getting in, but it would be tough to totally get rid of them.
Sincerely, Andy Love