VTVIPAKOUS DEVELOPMENT IN NOKTH. 49 



frequency. They also account for our inability to locate it in such 

 territory during the summer months. 



A careful search was made at different times for grasses that 

 were actually serving as summer food plants. The only hope of 

 finding such was in well shaded spots along streams, where, from all 

 indications, Toxoptera would be sufficiently protected to live and 

 reproduce throughout the summer. 



At Piano, Tex., Toxoptera was rapidly disappearing from the 

 fields in early June. By June 14 there was only a limited number 

 of plants which still supported the remaining few of these aphidids 

 and the latter were soon carried away by ants. When confined on 

 green food plants and protected from their enemies by a large frame 

 covered with thin cheesecloth Toxoptera lived until July 3. After 

 this date it was apparently too hot for their existence. Out in the 

 open, where young wheat and oats plants were sustained by frequent 

 watering, they lived until July 15. After this date they apparently 

 could not endure the summer temperature and no more were found. 

 Since no reinfestation appeared up to November 30, it was quite 

 evident that the aphidids had all perished. 



On June 28 viviparous forms of this species were found rather 

 abundantly in a small field of oats at McAlester, Okla. This field 

 of a few acres in size was on the east slope of a rocky hill. A natural 

 growth of timber surrounded the field and a few trees grew in its 

 midst where rocks make cultivation impossible. Green vegetation 

 was abundant in shaded places and along the creek one-half mile to 

 the east. Conditions of this sort are certainly favorable for Toxoptera 

 to five and reproduce throughout the summer as long as they find the 

 food plants present. While these spots, favorable to Toxoptera, are 

 characteristic of eastern Oklahoma, where, as has been stated, an 

 incipient outbreak of the pest actually occurred in 1911, they are 

 also found along streams in the central part of that State and in 

 northern Texas. As there appears to be no resting or egg stage in 

 the South, whenever there is a warm open winter these" aphidids 

 become very abundant and threaten the grain crops of this region. 



IN THE NORTH. 



Farther north, in the vicinity of Lafayette, Ind., viviparous repro- 

 duction is confined to the months of April, May, June, July, August, 

 September, October, and November. During mild winters, how- 

 ever, the species may breed viviparously throughout the year, as the 

 senior author found it breeding in the open throughout January, Feb- 

 ruary, and March, 1890, notwithstanding the fact that on January 24 

 the temperature fell as low as + 3° F.; on February 9, to + 6° F., 

 and on March 6 to + 4° F. It appears that a temperature of about 

 26675°— Bull. 110—12 4 



