Economic Threshold (ET) versus Economic Injury Level (EIL) definitions: which statement is correct?

• A. ET is the pest level of injury when controls should be applied to prevent reaching EIL; EIL is the economic loss caused by pest.
• B. EIL is the pest level of injury when controls should be applied to prevent reaching ET; ET is the economic loss caused by pest.
• C. ET and EIL are identical concepts.
• D. ET is the economic loss caused by pest; EIL is the pest level of injury.

Answer: (A)

The main idea is how we time actions to prevent economic damage. Economic threshold is the pest density at which you should start control measures so you don’t reach the level of damage that would cause economic loss. Economic injury level is the actual amount of damage, or the pest density at which the cost of the damage equals the cost of control, so beyond that point it’s not economical to tolerate more pests.

So the best description is that the threshold triggers control before reaching the loss level, while the economic injury level identifies the tipping point where the damage justifies the expense of control. In practice, you set the threshold below the injury level to allow time for a treatment to take effect and keep losses from becoming economic.