154 MISC. PUBLICATION 273, U. S. DEPT. OF AGRICULTURE 



INSECTS INJURIOUS TO FOREST RANGE PLANTS 



Grasses, herbage, and browse, which furnish feed to range ani- 

 mals, comprise a forest product sometimes of greater economic 

 importance or vahie than the trees that grow on the area. These 

 grazing plants may also suffer from insect attack and at times 

 are so completely destroyed in certain localities that cattle and 

 sheep have to be moved to other ranges. Moreover, the damage 

 to browse plants may carry over from year to year and reduce the 

 available feed for several years. Fortunately there are compara- 

 tively few insects that cause serious damage to range plants. 



The damage which grasshoppers may do to the grazing areas 

 is well known to everyone, and the insects themselves are such 

 common pests as to require no description. They are often par- 

 ticularly abundant in grassy meadows, where the females lay their 

 eggs in the ground, usually during the fall of the year, and new 

 broods emerge each spring to feed on all kinds of green and dry 

 vegetable matter. The nomnigratory grasshoppers remain in a given 

 locality and produce a new brood each year, under favorable con- 

 ditions becoming excessively abundant and destructive. Others are 

 migratory in habit and, after breeding to enormous numbers, and 

 having developed wings, travel across the country devouring every 

 growing thing in their ])ath. 



Much attention has been given to the control of grasshoppers, 

 and effective methods have been devised, the most satisfactory con- 

 sisting in spreading poisoned baits broadcast over the breeding 

 areas at about the time the young hoppers first come out and begin 

 feeding. A good bait consists of a mixture of 1 pound of white 

 arsenic, sodium arsenite, or paris green to 25 pounds of bran or 

 middlings, 2 quarts of blackstrap, and enough water to make a 

 thin mash. 



Periodically army worms, which are caterpillars of certain noctuid 

 moths, appear in countless numbers and advance over grazing areas, 

 devouring everything in their path. These also can be controllecl 

 to some extent by the application of poisoned baits similar to those 

 used for grasshoppers, or by ploAving trenches in front of the 

 traveling army of worms and killing them in the trenches by drag- 

 ging a log over them. Fortunately armyworm invasions on forest 

 ranges are not of very frequent occurrence. 



The Great Basin tent caterpillar (MaJacosoma fragilis Stretch) 

 appears from time to tim.e in the Great Basin area between the Kocky 

 Mountains and the Cascades and defoliates the bitterbrush {Purshia 

 trideiitata) ^ which is a most important browse plant for sheep in this 

 area. From 1928 to 1930 an invasion of this caterpillar swept over 

 the range country of eastern Oregon and northern California and so 

 seriously damaged the bitterbrush that it took several seasons for it 

 to recover, and the carrying capacity of the ranges was greatly 

 reduced. No practical control for this pest has been suggested, but 

 fortunately outbreaks are brought under control by natural enemies 

 after a few seasons of heavy feeding. 



The range caterpillar {Hernileuca oliviae Ckll.) {86) feeds on 

 wild grasses and sometimes on cultivated crops, and at intervals of 10 

 or 12 years is a serious range pest from Colorado southward into 



