Pests evolve resistance to our pesticides at an alarming rate. However, evolutionary theory tells us how we can slow the rate at which genes for pesticide resistance spread: by providing refuges where non-resistant insects thrive. Insects persistently nibble away at crops in the fields and at the narrow profit margin, they offer. What's a farmer to do? Spray, of course. Or, plant crops that have been genetically engineered to produce their own pesticides.