Rangeland Grasshopper Movement as a Function of Wind and Topography: Implications for Pest Management

Abstract

Monitoring rangeland grasshopper movements with a mark-release/ resight technique demonstrated that these insects have a tendency to move upwind in a native rangeland habitat with flat topography. This directional dispersal was observed with both late instar nymphs (4th and 5th instar) and adult grasshoppers, 60 h after release of marked individuals. Significantly more ofthe marked grasshoppers (34%) were in the northwest quadrant of the plots than in any other quadrant, and the wind was primarily from the northwest. At a native rangeland site with varied topography, where winds were also from the northwest, significantly more grasshoppers moved into the northwest quadrant than the southeast quadrant, 36 and 60 h after release; 35 and 32% of resighted grasshoppers were present in upwind quadrants, respectively. Grasshoppers showed no detectable tendency for movement with respect to topographic aspect in this habitat. An understanding of rangeland grasshopper movement in the context of abiotic factors (wind and topography) is relevant to refining grasshopper control programs that employ Reduced Agent-Area Treatments (RAATs).