Final answer:
The c) threshold stage is where the pest population level necessitates action to be taken, which often involves using pesticides with an ecological approach and as a last resort.
Step-by-step explanation:
When the level of a pest population reaches the stage where pest control action should be taken, this is known as the threshold stage. The threshold stage is critical because it's the point at which the pest population is dense enough to cause economic damage, or reach a level that is of health concern, and thus intervention is necessary. Prior to reaching this stage, monitoring occurs, which can involve scouting and identifying pest presence and levels.
The action taken once the threshold is reached may include chemical pest management, in which pesticides are utilized as a control measure, ideally as a last resort. Ecologically based control measures are always preferred, and when pesticides are necessary, products that minimize environmental impact, such as non-persistent pesticides, are favored. Effective pest management, including the decision to apply pesticides, should consider both the direct and indirect consequences on the ecosystem