Seasonal Losses in Rangeland Vegetation Due to Grasshoppers1

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Abstract
Livestock-free grazing areas were used for studies of grasshopper damage on Montana rangelands. Half of each study area was sprayed with an insecticide at the beginning of the season to eliminate nearly all grasshoppers. The grasshopper population remaining on the unsprayed portion of the-area was assessed by the use of cages that were placed over representative areas at night. Within both the sprayed and unsprayed portions of an area, sites were selected which appeared comparable from the standpoint of both the composition and abundance of the vegetation. Quadrats were established at these sites in which production was measured by clipping the vegetation at ground level, air-dried, and weighed. A comparison of the yield from an area without grasshoppers was thus made with that from an area on which grasshoppers fed. Little correlation was found between numbers of grasshoppers per unit area and the loss of vegetation. This may be accounted for by the differences in feeding habits of the various species comprising any particular grasshopper population. Further evaluation of the data from the various studies has proved more difficult. Problems have arisen primarily because of the nonrandom distribution of both grasshoppers and vegetation even where so-called uniform types of vegetation were considered. Difficulties in interpretation have also been encountered by the lack of knowledge concerning the phenomena of plant growth as shown by a study of two comparable areas during 1950-1959. These areas were subjected to grazing by livestock during the winter months only and the numbers of grasshoppers remained much below 1 per square yard during the period. Differences in yield of vegetation from the two areas were measured and it was found that considerable loss in forage may take place during a season without grasshoppers being present.

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