Economic Injury Level
The break-even point, where “A”=”B”, is known as the economic injury level. This is the population density at which the cost to control the pest equals the amount of damage it inflicts (actual or potential). Below the economic injury level, it is not cost-effective to control the pest population because the cost of treatment (labor plus materials) would exceed the amount of damage. Above the economic injury level, however, the cost of control is compensated by an equal or greater reduction in damage by the pest.
The economic injury level (EIL) is often expressed mathematically by the formula:
- “C” is the unit cost of controlling the pest (e.g., $20/acre)
- “N” is the number of pests injuring the commodity unit (e.g., 800/acre)
- “V” is the unit value of the commodity (e.g., $500/acre)
- “I” is the percentage of the commodity unit injured (e.g., 10% loss)
For the example given above, the economic injury level would equal 320 insects per acre:
The economic injury level is usually expressed as a number of insects per unit area or per sampling unit. Occasionally, when the insects themselves are difficult to count or detect, the economic threshold may be based on a measurement of injury (e.g., leaf area consumed or number of dead plants).
It is important to recognize that the economic injury level is a function of both the cost of pest control and the value of a commodity or product. Some commodities may be worth so little that it is never worth saving them from insect injury.
Different Values The value of other commodities may be so great that any level of infestation is worthy of control. Because of its dependence on both cost and value, the economic injury level can be calculated only after establishing a value for the damaged commodity or product. In practice, this can sometimes be a difficult task because different people have different values.