MONTANA INSECT PESTS, 1949 AND 1950 13 



WEIGHT OF GRASS CLIPPINGS 

 (Expressed in Pounds Per Acre Air Dry Weight) 



Grasshoppers Increase 



per First Second Third or 



Square Yard Clip Clip Clip Decrease 



Sprayed Area 



Wheatgrass Type Total <1 442 545 612 +150 



Needlegrass- 



Wheatgrass Type Total <1 660 800 696 + 36 



Unsprayed Area 



Wheatgrass Type 521 329 269 -262 



(a) Grass Feeders 4 



(b) Grass-Forb Feeders 2 



(c) Forb Feeders <1 



Needlegrass— 



Wheatgrass Type 564 516 316 -248 



(a) Grass Feeders 4 



(b) Grass-Forb Feeders 3 



(c) Forb Feeders 1 



The decline in weight of grass as a result of grasshopper util- 

 ization in the unsprayed area amounted to 262 pounds per acre in 

 the wheatgrass type and 248 pounds per acre in the needlegrass- 

 wheatgrass type, or 255 pounds per acre when expressed as an 

 average of the two. There was a gain in weight of 150 pounds 

 per acre on the wheatgrass type in the sprayed area, and 36 pounds 

 per acre on the needlegrass-wheatgrass type, which would give 

 an average figure of 93 pounds per acre. Total utilization by 

 grasshoppers would be the sum of the loss in weight on the un- 

 sprayed area plus the gain in weight on the sprayed area. This 

 would amount to 412 pounds per acre on the wheatgrass type and 

 248 pounds per acre on the needlegrass-wheatgrass area, an average 

 of 380 pounds per acre. If one were to assume that in the absence 

 of grasshopper utilization this range would yield the weight of 

 grass present on the date of the third clipping on the sprayed 

 area, the amount of grass consumed by 'hoppers would amount to 

 54% of the total yield. 



A 1,000 pound beef cow requires 22 pounds of air dry forage 

 per day which would amount to 7,920 pounds per year. Since 

 the 'hoppers removed 380 pounds of grass per acre, the forage they 

 removed from 20 acres of range would carry a 1,000 pound steer 

 for a year. The grazing capacity of this range runs about 35 acres 

 per head; hence, if grasshopper populations were eliminated, graz- 

 ing capacity could be increased by approximately 50%. 



