Approximately how many pesticide-resistant species were there in 1987?

• A. About 400
• B. About 150
• C. About 820
• D. About 900

Answer: (A)

Pesticide resistance is an evolutionary response driven by natural selection: when a pesticide is used, individuals with traits that help them survive at that chemical’s dose are more likely to reproduce, spreading those resistant traits in the population. By 1987, observations had accumulated across insects, weeds, fungi, and other pests, and the number of species showing resistance had grown to about four hundred. So, the option around 400 best matches the historical record up to that time, reflecting how widespread and rapid this evolutionary response had become with decades of pesticide use. The other numbers are farther from what was documented by then.