Which would increase the likelihood of pesticide resistance?

• A. Limiting the number of pesticide applications.
• B. An insect has only one generation per year.
• C. Applying a pesticide that has little or no residual effect.
• D. Continual use of the same pesticides from the same chemical class.

Answer: (D)

The choice that indicates an increase in the likelihood of pesticide resistance is based on the principle of selective pressure. When the same pesticides from the same chemical class are continuously used, it puts strong selective pressure on pest populations. This means that any pests that have, by chance, genetic mutations conferring resistance to that specific chemical will survive and reproduce. Over time, as these resistant individuals dominate the population, the effectiveness of the pesticide diminishes, leading to higher levels of resistance.

In contrast, limiting the number of pesticide applications can actually help manage resistance by reducing the frequency of exposure of pests to the chemical, thus allowing time for susceptible individuals to dominate the population. Similarly, having only one generation of insects per year limits the potential for rapid adaptation because there are fewer opportunities for the pests to reproduce and pass on any resistant traits. Finally, applying pesticides with little or no residual effect may reduce the effective concentration of the pesticide in the environment, thus providing less consistent selective pressure on pest populations. Therefore, the continual use of the same pesticides from the same chemical class is the most significant factor in fostering pesticide resistance among target pest populations.