6 



aphides that are all females and these in a short time begin to give birth 

 to living 5'oung which are likewise all females. Thus the life cycle 

 goes on, and though there is usually a radical change of food plant, 

 there are neither eggs nor males until autumn, when there is a genera- 

 tion consisting of both males and females, the latter depositing eggs 

 that winter over. This egg-laying female and the male are the un- 

 known forms of the leaf-aphis. 



Now, taking up the life history of the root-aphis, we find eggs in the 

 fall, it is true, but only in the burrows of and attended bv these ants. 

 If there are eggs, egg-laying females, or males elsewhere they have 

 yet to be discovered. The ants care for these eggs throughout the 

 winter, shifting them about, according to Forbes, as the}" do their own 

 young, to accommodate them to changes of weather and moisture. In 

 spring, the young, as soon as they hatch from these eggs, are trans- 

 ferred b}" the ants to the roots of young foxtail grass, smartweed, and 

 even ragweed. The young are carried out to pasture, as it Avere, dur- 

 ing fair weather, but in bad weather, or on cold nights, thev are taken 

 back to the burrows of the ants. The plants just mentioned are the 

 ones that push up earlj^ in spring in last year's corn lands, and espe- 

 cially in fields that have been plowed and allowed to stand untouched 

 for a week or so. Usually the farmer plows his ground in spring and 

 pays little attention to this earlj^ growth of weeds and grass, as he can 

 generally dispose of it as soon as he begins to cultivate the corn, 

 although this is not until the rows of 3'oung plants can be followed by 

 the eye across an ordinary field. As soon, however, as the corn plants 

 begin to show a))ove ground the ants not onlj" transfer the young 

 root-aphides from the burrows to the roots of corn, but they will also 

 remove them from the roots of grass and weeds and recolonize them 

 on the roots of 3'oung corn. Now these young aphides are all females 

 and within a few days they begin to give ])irthto young, also all females; 

 these, too, are cared for by the ants, which place them on the freshest 

 and most tender rootlets. This procedure goes on* about the roots of 

 corn througliout the spring and summer. Forbes has found that 

 under the most favorable artificial conditions there may be as many as 

 sixteen generations between April 8 and October 10, ten of which may 

 coexist at the same time. It is hardly pro])able, however, that so man}" 

 generations can exist under ordinaiv field conditions; nevertheless it 

 may be rightly inferred from this that the nudtiplication of the species 

 is enormous. These ants not only transfer the root-aphides from 

 one root to another of the same plant, ])ut will carry them from one 

 plant to another a considerable distance away. In the spring of 1887 

 the writer placed a number of flowerpots containing young, growing, 

 uninfested corn plants between rows of infested hills of corn in the 



[Cir.SG] 



