Diatomaceous earth or bed bug powders do not belong in your car. They are not the solution to your problem and can make you sick. It can get in your lungs, or your children’s or passengers lungs. Your car needs specialized treatment using pest strips, steaming and cleaning.
So repeat after me. I will not put diatomaceous earth in my car. But you might consider putting it under all your baseboards where you will either prevent an infestation or help to shorten one.