Injury equivalency as a basis for developing multiple-species economic injury levels
1988
A technique for developing and using multiple-species economic injury levels (EILs) is proposed, discussed, and evaluated. Grouping insects into injury guilds, based on the plant's physiological response to the injury, forms the theoretical basis for the multiple-species approach. In addition, a method for estimating crop injury, using an injury equivalency system, is proposed as a technique for refining the accuracy of EIL-based decision making. A detailed discussion concerning the theory and assumptions behind multiple-species EILs and injury equivalency is presented. As an example of the usefulness of the proposed system, we present data on a leaf-mass consuming insect guild on determinate soybeans. The paradigm includes an extensive review of defoliation-yield loss relationships for soybean and the calculation of EILs at four crop growth stages. Consumption data for five common soybean defoliators were also reviewed. These data were converted to equivalency coefficients based on the relative consumption potential of each species. With this system, each species within a guild can be related to every other species on the basis of its ability to contribute to overall injury. Finally, we present actual data for a leaf-mass soybean consuming guild and relate sampling information to the EIL. The result is a refined estimate of injury when species and size class consumption differences are incorporated in the estimate. Perhaps more significant, however, is the usefulness of the technique in assessing host injury, in economic terms, from multiple insect pests.
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