Cumulative Insect-Days as an Index of Crop Protection1

Abstract

Percent control is the usual index for the efficacy of an insecticide or other control measure against an insect. This places the emphasis on the proportion of the population that is eliminated. The magnitude and duration of the insects that survive treatment, however, is of greater importance to crop protection. Insect-days, the area under the curve of insect number on time, combines magnitude and duration into a single expression. The insect-days can be easily calculated from insecticide tests, and an example is given. Cumulative insect-days are suggested as an index of the crop protection afforded by a control measure.