9 
DISTRIBUTION IN THE UNITED STATES. 
The insect is usually common, and was found, during the present 
year, from Colorado and New Mexico to the Atlantic coast, approxi- 
mately covering the area south of latitude 41° and east of longi- 
tude 105°. Within this territory its area of destructive abundance, 
as well as the severity of its attack during any year, will be regulated 
by two factors: First, the presence of young growing wheat, vats, 
barley, or rye; and, second, weather conditions favorably to its rapid 
increase and unfavorable for the development of its natural enemies. 
It will breed freely in the fields from an altitude of less than 20 feet 
above sea level on the Atlantic coast to an elevation of nearly 5,000 
feet in Colorado, and from extreme northeastern North Dakota and 
Vic. 2.—The spring grain-aphis er “green bug” (Toxoptera graminum) : a, winged mi- 
grant; b, antenna of same; a, much enlarged; b, highly magnified. (Irom Pergande.) 
northwestern Minnesota, southern Wisconsin, northern Indiana, and 
southern Pennsylvania southward to extreme southern South Caro- 
lina and southern Texas. Yet, with normal weather conditions 
during the first four or five months of the year, these facts signify 
absolutely nothing, for this insect will not be abundant enough to 
attract any attention by its injuries. 
THE RELATION OF TEMPERATURE TO DESTRUCTIVE OUTBREAKS. 
In order to make the relation between temperature and destructive 
outbreaks of the “ green bug” perfectly clear it will be necessary to 
restate some of the facts given in Circular No. 85. 
This insect, as with other closely allied species of aphides, repro- 
duces in two ways. As cool weather approaches in autumn there 
occur in greater or less numbers both males and females, the latter 
[Cir. 93] 
