1909] 



Toxoptera graminum and its Parasites 



71 



If we assume that Southern Europe is the original home of the 

 species, its occurrence in the western hemisphere can only be 

 accounted for on the score of introduction, but the distribution 

 of the species in the eastern United States, does not in the least 

 indicate such an introduction as having come through any of the 

 Atlantic coast seaports. On the other hand, its occurrence all 

 along the Rio Grande River bordering Mexico, together with its 

 destructive abundance in northern Texas, as early as 1890, only 



z?/sr/?/Bur/o/^ or roxopr£/?A g/pa'^^wc/m /a/ theu/v/ted states. 



eight years after its first discovery in America, goes far to streng- 

 then the theory of an early introduction into some country to the 

 South, and a natural diffusion over the United States, following 

 the same lines of dispersion as for so many other species coming 

 to us from Mexico and southward. 



FOOD PLANT. 



The species is essentially a leaf infesting insect, rarely infest- 

 ing the stem. While preferring oats it will readily attack wheat, 

 rye, barley, and may often be found on the underside of the lower 

 leaves of corn. Corn excepted, its effect on the foliage of grain, 

 when present in large numbers, is to cause the infested leaves to 

 change to a red color, which seems to be very characteristic of 

 Toxoptera and does not follow, to a marked degree, attacks of 



