Which factor reflects the possibility that pests become tolerant after repeated exposure, leading to control failure?

• A. The pest developed resistance to the pesticide
• B. The LD50 of the pesticide is too low
• C. The rate of product applied was too high
• D. The restricted-entry interval was not followed

Answer: (A)

Pest resistance develops when pests are exposed repeatedly to the same pesticide, creating selection pressure that favors individuals able to survive. Those survivors reproduce, passing on resistant traits, so the population becomes progressively harder to control and the product’s effectiveness decreases over time. This is why repeated exposure can lead to control failure—the pest population shifts toward tolerance.

Having a low LD50 just means the chemical is highly toxic to pests, not that the pest population has become tolerant. Using too much product or not following the restricted-entry interval relates to safety, handling, and label compliance, not to the mechanism by which pests become less susceptible. To slow resistance, rotate products with different modes of action and follow label guidelines as part of an integrated pest management approach.