While prevention is always better than cure, the over use of insecticide, without any evidence of insects could work against you. Generally speaking, it has been due to the over use of pesticide/insecticide/herbicides, that resistance has become an ever challenging problem. The new school of thinking for managing pests is IPM - integrated pest management. What this means is, rather than rushing out to use chemicals, and possibly as suggested, even with no signs of pests, one uses a range of methods to manage potential outbreaks. There are a few methods, but I would be looking at Cultural practices - that is, keeping things clean, working safe and clean, not introducing anything which might cause problems etc. Biological control is also worth looking into, that is using traps/baits to lure insects to prevent them from living out their life cycle and thus stopping spread. As a good measure, yellow and blue sticky trap cards will monitor for a range of insects in a given area (specifically enclosed) and can help prevent outbreak or help to monitor infestation level. Only then would I think to start using any spray (petro-chemical or organic). Hope that helps