Economic Injury Level (eil) and Economic Threshold (et) Concepts in Pest Management

One of the fundamental concepts of integrated pest management is that each pest species has a definable relationship in terms of damage to the plant or animal host that it attacks. This relationship is often referred to as the damage curve (Fig. 1), which is often determined relative to yield loss. This damage curve can take several forms, but was summarized by Higley and Peterson as having a tolerance or overcompensation phase ([1] no yield response, or [2] positive yield response to injury), a linearity phase ([3] e.g., yield loss = -a (unit injury) + b), and a desensitization and an inherent impunity phase ([4] decreasing and finally [5] no additional yield loss per unit injury). The curve can be used with various methods to determine whether or not any action or pest management tactic (e.g., pesticide, biological control, cultural control, etc.) is needed to reduce the damage associated with this pest. Also, this relationship is uniquely characterized by a critical point, the economic injury level (EIL), or the point in the agricultural production system where the costs associated with pest management equal the benefits from the pest management actions. In other words, below the pest population represented by the EIL there is no need to take pest control actions because they are not economically justified, but onomic damage can occur when the pest population densities are above the EIL. A simple, robust model of the EIL relationship between pest control costs and benefits from control actions was developed by Pedigo et al. as: