What is a sign that pest populations have developed resistance to a pesticide or resurged after treatment?

• A. Pest populations rebound after initial suppression.
• B. Pests are completely eliminated.
• C. No pests exist.
• D. Pests never respond to any pesticide.

Answer: (D)

Resistance shows up when pest numbers rebound after treatment. If a pesticide initially suppresses the population but then the pests come back—often at the same level or higher—it indicates that some individuals survived the spray and those survivors repeated and repopulated, spreading the tolerant traits. That rebound is the clearest sign that the control method is losing effectiveness due to resistance.

Elimination or no pests exist means the treatment worked, not that resistance has developed. The idea that pests never respond to any pesticide is not a realistic field sign; failures can stem from misuse, timing, or targeting a product the pests aren’t susceptible to, rather than true universal resistance.