146 MISCELLANEOUS PAPEES. 



pennsylvanicum, and Panicum 'pToliferwnii^ which plants were then 

 dead. December 9, there were a few on the sorghum and corn, these 

 being the only plants alive at that time. When examined about a week 

 later all plants in the cage were dead and no aphides could be found. 

 It might be mentioned that this cage was kept at the outdoor tem- 

 perature. This aphis shows a decided preference for broom corn over 

 Indian corn and sorghum. Both in the field and in the insectary 

 aphides which had been living on sorghum plants for a nmnber of 

 generations always changed to broom-corn plants when these were 

 placed in the cages. 



LIFE HISTORY. 



As stated above, we do not know where and how this aphis passes 

 the winter. In Illinois it first appears in midsummer, the earliest 

 date being June 2G, 1906, at which time Mr. E. O. G. Kelly found it 

 quite numerous on broom corn at Mattoon, in central Illinois. We 

 know that it reproduces parthenogenetically from the time of its 

 first appearance in the fields until its disappearance in the fall. In 

 the fall, so far as has yet been observed, these aphides gradually 

 die off as freezing weather comes, leaving neither eggs nor hibernat- 

 ing adults upon or about the corn plants. I did not make au}^ ob- 

 servations in the field in 1900, but in 190.5 (a more severe season than 

 1906) I found living xiphis maidis on sorghum as late as October 28, 

 and all found at that date were either winged or the pupge of winged 

 viviparous females. Numerous experiments have been made by 

 Doctor Forbes and his assistants to determine the manner in which 

 this species hibernates, and whether or not there is a sexual generation 

 in the fall, as is usually the case with aphides. Since these investi- 

 gations were thorough, it seems possible that the aphides may not 

 spend the winter in the Qgg stage, at least in central or northern 

 Illinois. There are at least two permissible suppositions as to the 

 winter history of these insects. T\\qj may hibernate as adults in 

 the warmer States, or even in southern Illinois, and, as the summer 

 progresses, gradually diffuse themselves to the North with the ad- 

 vance of the season and infest the plants in these northern States. 

 This supposition is plausible, inasmuch as this species has been found 

 in Mississippi on barley in January; but the fact that aphides are 

 probably unable to travel great distances is against it. No work 

 has been done as yet on this line of investigation, and it is possible 

 that if one began his search for this aphis in the far South — even 

 in the southern part of Illinois — he would find it at a much earlier 

 date than it has heretofore been reported, and that he could follow 

 its gradual diffusion northward. The other and more likely theory 

 is that, like many aphides, it has an alternate food plant on which 

 it passes the winter and spring. 



