stances, a comparatively few females may become the progenitors of 

 the enormous swarms of these insects that overrun and destroy fields 

 of grain over vast areas of country. 



FOOD PLANTS. 



The writer lias found this grain-aphis breeding freelj' on wheat, rye, 

 oats, barley, and corn, though it seems to prefer wheat and oats. 

 Orchard grass ( Dacfylis glonierata) seems to suit the taste of these 

 insects almost as well as wheat, and it is probably to this and some 

 other grasses that the winged females migrate when they forsake the 

 grain fields in June. 



Although the writer failed to rear the insect from Eragrostis, Panicum, 

 Ixophorus (Setaria), Agrostis, and Bromus, it is quite probable that it 

 may l)e found on some of these, as it is known to occur on some of 

 these grasses in Europe. Rondani gave as food plants oats, wheat, 

 spelt, couch grass, Hordeum nmrmuni, soft chess {Bromus Iwrdeaceus) , 

 and corn. In 1863 Passerini added sorghum, and in 1900 Del Guercio 

 gave the food plants as wheat, barley, oats, corn, orchard gra.ss, Bronms 

 sp., and Lolium perenne. It seems quite likely, therefore, that the 

 present list of this insect's food plants in America maj' in future be 

 considerably enlarged. 



DISASTROUS OUTBREAKS IN AMERICA. 



While more or less common every year, the occurrences of this grain- 

 aphis in such destructive abundance over such a large area of countr}- 

 at such long intervals of time are somewhat puzzling phenomena. 

 When first met with by the writer, in 1884, the insect in question was 

 not at all injurious, and it was more than five years later that it was 

 again encountered — this time as a serious pest. This was the outbreak 

 of 1890, which proved so disastrous to wheat and oats over a section of 

 country extending from Texas to northern Missouri, through southern 

 Illinois and Indiana to eastern Kentucky and Tennessee. Oats were 

 destroyed as far north as Franklin, Ind., latitude 89^^ 80'. Though 

 quite abundant at times, this aphis did not again cause serious injury 

 until in 1900, when the Southwest again suffered an outbi'eak which, 

 while even more serious in Texas than was the one in 1890, did not 

 extend so far northward. The present year (1907) there is every indica- 

 tion of a recurrence of the pest, for as early as Januiuy this insect was 

 reported by Mr. W. I). Hunter, of this Bureau, as destroying the fall 

 wheat and oats in northern Texas. 



NATURAL ENEIVIIES. 



Not only is this aphis enormously parasitized, but toward the last of 

 May and in early June both young and old are devoured by lady beetles 

 and thf'ir larva\ great numl)ers of wliich can be ol)served at work in 



