Estimating the Abundance of, and Damage Done by Grasshoppers

Because of extreme activity the numbers of grasshoppers, Acrididae, are hard to estimate. By aid of a field glass the observer can stand at some distance and count those in a given unit. Many units of ground should be so counted in a field before an estimate of the grasshoppers can be made. A knowledge of the egg laying habits is necessary before an estimate of the number of eggs in a locality can be made. Estimating the per cent of damage in a particular field is done by comparison of the amount of damaged seed in several small units with the undamaged seed. When making up a statement of the damage done by grasshoppers over a wide area, the entomologist should, when possible, compare the yield of damaged sections with the yield of localities where there were no grasshoppers but which had other limiting factors equal. A comparison of the yield during the grasshopper infestation with the yield in the same localities but in years when there were few, if any, grasshoppers can be made but before the entomologist can estimate the damage done by grasshoppers, he must know the action, during the years under comparison, of other limiting factors such as rainfall, temperature, sunshine, winds, and crop diseases.