Hi Cancan
A friend of mine who is an entomologist (insect expert) at Murdoch University (Perth) once reminded me of one major factor that comes with most insects. They rely on odours for communication, searching for food, almost everything. Something as simple as vinegar will stuff their scent trails up, and prevention being better than cure, I have often used vinegar around the base (tyres and such) of storage areas, and have never had a problem with insects.
Regards
Tjupurula