Answer:
Mutation.
Step-by-step explanation:
Mutation is the factor that is responsible for the acquiring resistance of various pests against pesticides because in mutation the genetic makeup of the organism changes which has no effect of the chemicals applied on them. Repeated use of the same type of pesticides to control a specific pest can cause changes in the genetic makeup of a pest that leads to another form of pest which causes pesticide resistance in the new type of pest so we can say that mutation is the main cause of resistance in pests.