BIOLOGICAL STUDIES ON THREE APHIDID^. 145 



account of its injuries to corn. Although since that time considerable 

 w(!rk has been done on this aphis, we do not yet know how it spends 

 the winter. In 18G2 Mr. Benjamin D. "Walsh found an aphis living 

 on the roots of corn about Rock Island, 111., and, although he was 

 doubtful as to its identity, he distinguished it by calling it the root 

 form of Aphis maidis. From that time until 1891 these two forms 

 were supposed to be the same species, until Doctor Forbes, who had, 

 since his first knowledge of them, regarded them as probably two dis- 

 tinct species, named the subterranean form Aphis m.aidi-radicis in the 

 Seventeenth Report of the State Entomologist of Illinois. 



Aphis maidis has always been considered more or less injurious to 

 corn, sorghum, and broom corn, although it seldom becomes seriously 

 so. In some cases, however, it injures the corn ears by sucking the 

 sap from the silk and killing it, thus preventing fertilization of the 

 kernels. Only rarely, however, does it stunt the growth of the plant, 

 at least in Illinois, the reason probably being that in this State the 

 aphis does not commence its attacks upon the plant until the last part 

 of June or the first of July, at which time the plant is strong enough 

 to withstand the drain made upon its sap supply by the aphis. This 

 aphis sometimes does considerable injury to the quality of the brush 

 of broom corn by discoloring it, the discoloration being " clue 

 to a bacterial affection following upon the plant-louse punctures " 

 (Forbes). 



This aphis has a very wide distribution, being found in all parts of 

 the United States where corn is grown; that is, from Maine to Cali- 

 fornia and Texas. Prof. F. M. Webster has reported finding it on 

 sorghum in Australia, where, he says, it is sometimes quite obnoxious, 

 and in a recent circidar he says that " the insect is also known from 

 Japan."" 



FOOD PLANTS. 



Though the usual food plants are corn, sorghum, and broom corn, 

 this species feeds also on various other plants, as barley, Setaria 

 glauca-i and Oxalis. At Urbana, 111., September 7, 1906, in an in- 

 fested cornfield, I found Aphis maidis also breeding on Panicmn 

 cnis-galli and Panicumj sanguinale. 



In our insectary, in 1906, plants of Fanicum crus-galli and Pani- 

 cumj sanguinale^ which had accidentally grown up in some unused 

 pots, became almost covered with Aphis maidis. Numbers of these 

 aphides were placed in a Comstock cage containing the common weeds 

 found around cornfields, namely, Setaria glauca, Panieum crus-galli, 

 Polygonum pennsylvanicum, Panieum proliferum, Panicuni sangui- 

 nale, broom corn, sorghum, and corn. Wlien examined two days later 

 (September 10, 1906) the aphides were breeding freely on all plants 

 except corn, which was at that time just sprouting. November 1, 

 aphides were on all plants except Panieum crus-galli, Polygonum 



