Diatomaceous Earth

Diatomaceous Earth is an incredibly versatile, natural product. It is literally earth, or dirt. But it's a special kind. It's formed by tiny crystals with incredibly sharp edges that are invisible to the human eye. However, those sharp edges will dry your hands out if handled with bare hands too much - and they'll carve the exoskeleton of an insect up in a heartbeat. Which of course results in the death of the insect that crawls through the dust particles of Diatomaceous Earth.

It's not a poison - so they can't develop immunity. The only downside is once it gets wet, it's relatively useless at that point, so it has to be applied frequently, especially after rainy or humid weather.