Investigation of grasshopper collection methods to improve pest management in Montana cropping systems

Pest grasshopper species in the family Acrididae can be devastating to many crops. In addition to direct feeding, they have the potential of causing greater yield loss by damaging plant stems, leading to premature detachment and wastage. To assess the need for management interventions against grasshopper pests, it is important to correctly estimate their population density through systematic scouting and monitoring processes. Three main collection methods are commonly used to estimate grasshopper abundance in cropland and include visual counting, sweep netting, and pan trapping. Visually counting can be difficult once the crop gets big enough to obstruct the view of the area. Pan trapping is done by placing a pan in the ground and passively waiting for samples to jump or fall in. Sweep netting is done by actively passing a net over the collection area and collecting the grasshoppers that jump in. Pan trapping and sweep netting seem to be the best methods to estimate grasshopper abundance and diversity. Each collection method may be biased toward certain stages of grasshoppers. Pan trapping might be more effective for collecting nymphs because they are found close to the ground, while sweep netting might be more effective for collecting adults because they have wings to assist in jumping higher. This study reports the results of a comparison between grasshopper sampling methods. Collections were made in Montana cropland from plant emergence to harvest and included sampling of nymph and adult life stages of a complex containing multiple grasshopper species.