What is the primary reason pesticide resistance develops?

• A. The presence of a resistant biotype within the normal population
• B. Overuse of water
• C. Pesticide drift
• D. Excessive rainfall

Answer: (A)

Resistance emerges primarily through natural selection acting on genetic variation in the pest population. Some individuals naturally carry genes that make them less affected by a pesticide. When the field is sprayed, susceptible pests die while those with resistance survive and reproduce, passing the resistance genes to their offspring. Over generations, these resistant traits become more common, and the pesticide becomes less effective.

The other factors listed don’t create resistance themselves—they influence exposure or how the pesticide is distributed. Overuse of water, drift, or heavy rainfall can affect how much pesticide pests encounter, but the genetic adaptation that reduces susceptibility comes from selecting for preexisting resistant individuals in the population.