When the foliage of the cultivated grains becomes too old and tough- 

 ened to afford them sufticient nourishment, the j'oung — as is usual 

 among aphides — develop to winged viviparous females (i. e., winged 

 females that give birth to living j'oung, fig. 1, a) and forsake the grain 

 fields. Thus it is that the migration from the grain to the alternate 

 food plant takes place in June, while in the fall of the year the aphides 

 return to the fields instead of leaving them, although the latter is the 

 rule with most of the other species whose habits are well known. It is 

 this variation from the usual habits of allied species that renders this 

 particular aphis so destructive in grain fields and its control so exceed- 

 ingly difficult. 



With the appearance of the young grain in the fields in autumn the 

 aphides again appear, being represented by winged females that soon 

 begin giving birth to young, and various sizes of the latter according to 

 age may frequentlj' be observed surrounding the mother on the leaves. 



Fiii. ■2— The sprini; Kiain-aiihis (Toxnptera graminum) : a. wintrle.ss female: b, larva; 

 c, pupa. Much enlarged (original). 



Young develop to adults and themselves begin to reproduce Avithin the 

 space of a week, so that in favorable weather several generations may 

 be fully represented on the same plant by young of all ages and winged 

 and wingless females. 



RAPIDITY OF INCKEASP]. 



In experiments with a winged female in April, in Indiana, the writer 

 obtained 37 offspring within the period of eighteen days, and at the 

 end of this time some of her firstl)orn were themselves grandmothers. 

 From the writer's experience with allied species it is probable that the 

 wingless female is much more prolific than the winged female, so that 

 it would be entirely within reason to suppose that a wingless mother 

 would be capable of producing at least double the number of young 

 mentioned above within a slightly more extended period of time. 

 It will thus be seen that within a brief period, under favorable circum- 



