190 



INSECTS INIUKIOUS TO VEGETABLES 



a lack of thrift and vigor, arc the outward manifestations of 

 injury. Another indication is the presence of numerous small 

 brown ants which attend this species and without which it 

 probably could not exist. 



The corn root-aphis is bluish green, slightly whitened by a 

 waxy bloom. The body is oval, and the nectaries are erect or 



Fig. 12 1. ^Winged viviparous female of corn rooi-aphis; wingless egg-laying female. 

 Enlarged. (After Forbes) 



project slightly backwards. Two of the different forms arc 

 shown in figure 121. It is found from Massachusetts to Minne- 

 sota and Nebraska and as far south at least as Virginia. 



The winged forms migrate to various weeds, among which 

 are smartweed, pigeon grass, mustard, pigweed and plantain. 



Economic Treatment. — Our present knowledge of this insect 

 suggests several methods of attacking it. Crop rotation and 

 care not to plant in or near fields of weeds which serve as 

 alternate hosts ; the free use of manures and other fertilizers to 

 stimulate the growth of the plants; the disturbing and destruc- 

 tion of the nests of the protecting ants; the destruction of all 

 of the weeds which serve the aphides as food early in the 

 season by plowing, and, in connection with this, late planting 

 of corn.^ Such measures of procedure may not entirely pro- 

 tect the crops in all localities in all seasons. 



' These and other remedies are considered in detail by F. M. Webster in 

 Circ. 86, Bu. Entom., U. S. Dept. Agr. 



