2 MISCELLANEOUS PUBLICATION 1348, U.S. DEPARTMENT OF AGRICULTURE 
make. The following tabulation shows the benefits 
from spraying on two rangeland areas with differ- 
ent carrying capacities, using cost of hay for com- 
parison. 
Cost of hay 
Item 
$22.22/t $27.78/t $33.33/t 
Carrying capacity at 8ha/AUM: 
Value per hectare 9.13 11.40 13.70 
Less cost of control per hectare _1.88 1.88 1.88 
Benefit from spraying 7.25 9.52 11.82 
Carrying capacity at 12 ha/AUM: 
Value per hectare 6.08 7.60 9.10 
Less cost of control per hectare 1.88 1.88 1.88 
5v72 7.22 
Benefit from spraying 4.20 
This tabulation is based on an animal unit con- 
suming 8 to 9 kilograms of dry feed per day. Pfadt 
(1949b) used similar reasoning to estimate that a 
savings of $11.50 per hectare could be made by 
spending $2.25 per hectare to kill the grasshoppers 
in Wyoming. He also pointed out that cattle and 
sheep have an increase in weight (gains) when they 
do not have strong competition for forage. A 
rancher may make plans to have his pasture mod- 
erately grazed by livestock, when in fact if it 
contained 18 grasshoppers per square meter, the 
grazing would be extremely heavy. Bullen (1966) 
mentioned that modern control methods are expen- 
sive, and to justify this expenditure or at least put 
it into economic perspective, it is necessary to eval- 
uate the effect of grasshopper damage upon agricul- 
tural production and its consequent effect upon the 
human economy of the infested area. The same au- 
thor suggested that damage to grazing land is diffi- 
cult to assess quantitatively and even when as- 
sessed, difficult to express in economic terms. In 
semiarid regions, yields may vary greatly from 
year to year and depend principally on rainfall. To 
evaluate the quantitative effect of grasshopper 
damage, it is necessary to forecast the yield. Bullen 
(1972) also stated that grasshopper injury becomes 
economic damage when the yield of the crop is ad- 
versely affected, quantitatively and (or) qualita- 
tively. The assessment of such economic damage is 
no easy task, and many factors have a bearing on 
vegetation losses caused by grasshoppers in the 
Western United States. 
In 1973, I searched for ways of determining ac- 
tual forage losses caused by rangeland grasshop- 
pers. The main objective was to predict early in the 
spring the forage losses that would occur in the 
summer and later on in the fall if grasshoppers 
were not controlled. I soon realized that many other 
researchers had approached the same problem, and 
information was widely scattered. I, therefore, re- 
viewed the more important papers that contribute 
to this subject. Presented here is a brief evaluation 
of the factors that contribute to forage losses 
caused by rangeland grasshoppers and also results 
of some of the studies in terms of estimated 
amounts of forage destroyed by grasshopper popu- 
lations and species. I hope that this review will be 
useful to other entomologists researching this prob- 
lem and will benefit those agencies and individuals 
who must make decisions on economic control. 
FACTORS AFFECTING FORAGE CONSUMPTION BY 
GRASSHOPPERS 
Food Preference 
More than 600 species and subspecies of grass- 
hoppers are in the United States, many with spe- 
cific food preferences. However, not all of the spe- 
cies are of economic concern since some never 
become abundant, others are restricted to isolated 
habitats, and a few may be classified as beneficial. 
For example, Ball (1936) claimed that out of 130 
species of grasshoppers occurring in Arizona and 
130 occurring in Colorado only 5 or 6 should be clas- 
sified as injurious to crops, and scarcely a dozen 
more should be listed as serious pests of rangeland 
vegetation. 
A Kansas study (Jantz 1962) with Melanoplus 
femurrubum (DeGeer) concluded that this grass- 
hopper is probably of more economic importance as 
a beneficial insect rather than harmful on range- 
land; however, it was found to be a crop pest, par- 
ticularly on alfalfa. Burkhardt (1959) suggested 
that chewing insects such as grasshoppers may 
effectively prune the plants, resulting in plants 
with increased vigor and growth. Anderson (1970) 
stated that clipping studies indicate, under certain 
