THE CORN ROOT- APHIS AND ATTENDANT ANT. 33 



that optimum conditions might continue in an occasional instance 

 for as much as three successive generation periods, and it may help 

 us to understand the facts sometimes observed if we know that the 

 product of reproduction for these three generations under such con- 

 ditions would amount to about 66,000 descendants for each female. 



The average number of young produced in our experiments by 

 a single female in a single day was 4, and the largest number was 12. 

 The time elapsing from the birth of the female to the birth of her 

 first young varies from 21 days in early spring to 6 days in August. 

 For a series of 10 generations, beginning June 23 and ending with 

 the appearance of the sexual oviparous generation in fall, the aver- 

 age age of the female at the birth of her first young was 7.8 days, 

 at the birth of her last young it was 16 days, and the female may 

 live from 1 to 6 days longer. The average total life period of a 

 viviparous female was about 24 days, although 30 to 35 days is not 

 unusual. The oviparous generation is rather longer lived, the aver- 

 age for 15 individuals being 26 days, with a maximum of 61. Life 

 is longer, growth is slower, and reproduction more deliberate in the 

 cooler parts of the season, both spring and fall, than in the warmer. 

 An aphis isolated September 18 began to reproduce in 11 days, 

 brought forth young — 56 in all — for 31 days, and died November 7 

 at the good old age of 51. 



THE ATTENDANT ANT. 



The absolute dependence of the corn root-aphis upon its attendant 

 ants is doubtless well understood. It is almost invariably found in 

 charge of that most abundant of all American ants, Lasius niger 

 americanus, the commonest ant of pastures, meadows, and cornfields 

 throughout the greater part of the United States. The life history 

 of this ant was fairly well given by me in the eighteenth report of 

 the State entomologist of Illinois. 



It hibernates underground in the fields in comparatively small 

 colonies of workers, 50 to 200 or more in each, often with larvae of 

 various sizes and sometimes with eggs. A queen will occasionally be 

 found among the hibernating workers, although eggs are sometimes 

 laid by isolated queens for new colonies in fall. The queen seems 

 sometimes to spend the winter entirely alone or else to leave the old 

 colony very early in spring. April 7 of this year, for example, a 

 queen ant was found in a cornfield in her cell, alone, with neither 

 eggs nor aphides near her. Pupation begins during the latter part 

 of May in central Illinois, and winged sexual forms, male and female, 

 begin to emerge about a month later and continue to appear from time 

 to time at least until October. 

 31024— No. 60—06 m 3 



