12 BULLETIN 112, U. S. DEPARTMENT OF AGRICULTURE. 



17 mother plant-lice was 22.1 young; and in 1912 the average for 43 

 individuals was 32.7 young, with a range of from 12 to 65 young 

 per female. There was thus an average for the three years of 32.3 

 young. The largest number of young produced by a single female 

 was 103, and normally, in the cooler parts of the year, the number 

 ranged between 50 and 60. The number of young produced per 

 day ranged from 1 to 8 per female, and the length of the period from 

 birth to maturity varied from 6 to 15 days and averaged about 8£ 

 days, excepting in late fall, when the length of time was ordinarily 

 much greater. According to the numerous tests the species molts 

 but four times, as do other species. 



It will be seen from the foregoing that this species-, like many 

 other plant-lice, is quite prolific, although not so prolific as the 

 "green bug" (Toxoptera grawAnum). It is computed that in 15 

 generations, averaging 30 young per female, the progeny from a 

 single individual, providing all lived and reproduced, would cover 

 almost the entire land area of the world, or, if packed 256 to the 

 square inch and piled 25 high to the inch (6,300 to the cubic inch), 

 would cover the entire State of Texas to a depth of 7 inches. For- 

 tunately plant-lice are delicate insects, being highly susceptible to 

 rains and inclement weather, and are preyed upon by many preda- 

 ceous and parasitic animals, as well as being subject to fungous 

 diseases. 



In 1879 Dr. Cyrus Thomas 1 aptly discusses the winter habits 

 of the wintering viviparous females in the following words : 



When winter appears they move down toward the ground, some of them, at 

 least, entering the soil and feeding upon the sap of the roots. At any rate, I 

 find the apterous ones at this time working upon the roots, but at the same 

 time I find a winged individual above ground. I have also observed them 

 heretofore at the root of the wheat, late in winter, while snow was on the 

 ground ; and what somewhat surprised me. I found them busy at work under 

 the snow, and the apterous females bearing well formed larvse. 



There are numerous office records in which the occurrence of this 

 plant-louse is reported on wheat and grasses during the winter 

 months, but the following individual record will substantiate the 

 belief that the insect may survive even rather severe winters as 

 viviparous females. At Wellington, Kans., Mr. T. H. Parks found 

 adult wingless viviparous females of the oat aphis on wheat roots 

 April 9, 1910, and these had undoubtedly passed the winter on wheat, 

 or were the direct progeny of overwintering females. The winter 

 of 1909-10 was an unusually severe one at Wellington, according 

 to Mr. E. O. G. Kelly, the ground becoming frozen early in Decem- 

 ber, 1909, and remaining frozen until February, 1910, after which 



1 Eighth Rept. State Entomologist, 111., 1879, p. 53. 



