Which factor influences the development of resistance in a pest population?

• A. Frequency of preexisting resistance
• B. Time of day
• C. Color of pests
• D. Amount of rainfall

Answer: (A)

Pest resistance develops when natural genetic variation for resistance already exists in the population and pesticides apply a selective pressure. If some individuals happen to carry alleles that let them survive a pesticide spray, those survivors reproduce and pass those resistance traits to their offspring. With each round of exposure, the proportion of resistant individuals grows, so resistance becomes more common in the population over generations. The more resistance-genetic variation present before exposure, the faster resistance can emerge.

Time of day, color of pests, or amount of rainfall don’t change the genetic makeup of the population, so they don’t directly drive the development of resistance. Time of day might affect when pests are active or exposed, and rainfall can influence pest numbers or pesticide fate, but neither alters the frequency of resistance alleles in the population.