and is not considered in the present estimates. Losses due to this 
sawfiy are caused by reduced weight of the wheat kernels from tun- 
neling of the stems by the sawfly larvae, ard the breaking over of 
stems girdled by the insect. When the stems are broker:, the wheat 
heads cannot be recovered during harvesting. 
Control of the sawfly depends on such cultural practices as early 
harvesting, shallow cultivation or deep plowing, crop retations, 
ard the use of resistant creps. Insecticices have not, proved practical. 
Grasshoppers 
Since pioneer days grasshoppers have caused extensive lesses to 
crops and rangeland in the United States (for losses to rangeland 
by grasshoppers see Chapter VI). Threnghout the growing season, 
these insects feed on small grains, corn, cotton, flex, alfalfa 
and clovers, and other crops, They reduce yields by defoliating 
the plants, biting off grain heads, flax and cotton bolls, and 
interfering with pollination by eating corn silks ard the flowers 
of alfalfa and clovers. 
Hundreds of species of grasshoppers occur in the United States, 
but many of them are of little economic importence, Five cf the 
most important species attacking crops west of the Mississippi 
River are the migratory grasshopper, differential grasshopper, 
two-striped grasshopper, red-legged grasshopper, and the cleare 
winged grasshopper. The devastating grasshopper sometimes attacks 
crops in California. Over the period 192-51, these species caused 
an estimated annual loss of about $18,000,000 to crops. During the 
same time, crops worth an estimated $35,000,000 were saved snnuelly 
by the application of contre] measures. 
In the Southeastern States the American grasshopper is « serious 
crcp pest, and threughout the rest. of the country east of the 
Mississippi River several species of grasshoppers do a large amount 
of damage to crops. No satisfactory data are currently avsilable 
which would permit a reliable estimate of this less. 
The contrel of grasshoppers has changed completely during the 
last few years. New insecticices appiiad as sprays or dusts have 
replaced poison baits, providing more effective kills, even with 
low dosages of the toxicant. Today ar application cf only 2 ounces 
of aldrin in one gallon of oil per acre practically eliminates 
the infestation. In addition, aircreft and ground equipment have 
been improved to provide more efficient end economical means for 
applying the insecticide over large areas. 
Sugar Beets 
Sugar-beet crops are attacked by mary insects. The most destriuce 
tive is the beet leafhopper, the only carrier sf the curly top 
virus. Direct damage by this leafhoprer is usually nesligible, but 
