Repeatedly using the same insecticide — particularly one with the same mode of action (MOA) — is the most effective way to accelerate the evolution of pest resistance.
Each time an insecticide is applied, natural genetic variation means a few individuals in the population are naturally resistant.
The susceptible individuals are killed; the resistant ones survive and reproduce.
After several generations of this selection pressure, the resistance genes become fixed in the population, leading to the entire population becoming resistant.
This process develops extremely rapidly in pests — because they have short reproductive cycles and large population sizes.
Strategies to slow down resistance include: rotating insecticides with different MOAs — use a pyrethroid (sodium channel) this time, a neonicotinoid (nAChR receptor) next time, and an IGR (chitin synthesis) the time after that.
Do not use sub-lethal doses — using less than the recommended dose accelerates the selection process.
Integrate non-chemical methods — physical exclusion, sanitation, sticky traps — to reduce reliance on chemical agents and lower the selection pressure for resistance.
This is also the core philosophy of Integrated Pest Management (IPM).