Which would increase the likelihood of pesticide resistance?

The continual use of the same pesticides or pesticides from the same chemical class significantly increases the likelihood of pesticide resistance developing in pest populations. When pests are repeatedly exposed to the same chemical mode of action, they are more likely to survive through natural selection. The individuals that possess genetic variations allowing them to survive that particular pesticide are more likely to reproduce, leading to a population that is increasingly resistant.

This phenomenon occurs because pesticides often target specific biological pathways or processes within the pests. Over time, as susceptible individuals are killed off, the surviving population becomes more resistant. This resistance then gets passed down through generations. By continually using the same pesticide or those from the same chemical class, the selection pressure is constant, making it easier for resistant individuals to thrive.

In contrast, applying pesticides with little or no residual effect may reduce the likelihood of resistance as they may not persist long enough in the environment to exert a consistent selection pressure. Limiting the number of applications or having pests that have only one generation per year also do not create the sustained pressure needed for resistance development, as these factors can decrease the likelihood of pests being exposed to the same chemical repeatedly throughout their life cycles.