194 The Sugar-Beei in America 



and attack sugar-beets only incidentally. Grasshopper 

 injury varies greatly from year to year, usually increasing 

 gradually up to a climax year and then dropping off sud- 

 denly to begin the gradual ascension again. At least a 

 dozen species are known to attack sugar-beets. 



Grasshoppers are commonly kept within normal num- 

 bers by natural enemies, among which are birds, fungous 

 diseases, and other insects. Mechanical means of coping 

 with them, such as that shown in Plate XXI, are also used. 

 Plowing under the eggs before they have had time to 

 hatch is probably the most effective means of controlling 

 them when the breeding grounds can be handled in this 

 way. Several t\'pes of catchers are also used with success. 

 Arsenic-bran mash is the most economical and effective 

 poison. 



Beet-root aphis {Pemphigus hetae Doane) . 



Within the last few years the beet-root aphis has spread 

 rapidly over the beet-grox^dng sections of the United 

 States. Attention was first called to it in 1896. It is 

 similar in appearance to its relative, the woolly aphis of 

 the apple. The insect lives on the small roots of the beet, 

 sucking juice from it and thereby dwarfing the plant. It 

 protects itself by means of its woolly covering and is 

 consequently not injured by irrigation water. At inter- 

 vals a generation of winged indi\'iduals appears ; these 

 fly to other fields, where they settle doTSTi and begin a 

 new colony. In the fall, winged females fly to cotton- 

 woods and lay eggs on the trunks. These hatch in the 

 spring and migrate to leaves, where they pass one or more 

 generations before going to the beet fields. In Colorado, 



