are born alive, after the manner of nianimals, and all are fertile 

 females. It will therefore be ver\' clear that with no knowledge of 

 the males and with only this fragment of the life ('\'cle of the females 

 it is impossible to say whether the leaf -aphis is an above-ground form 

 of the root-aphis or whethei- it is distinct from and wholly inde- 

 pendent, of that insect. 



FIELD EXPERIMENTS. 



In October, 18S5, the writer transferred some volunteer plants of 

 corn from the field of fall wheat, where they were growing, to some 

 breeding cages. The plants were thickly populated with winged 

 females of the leaf -aphis, and these were carefull}' secured with the 

 plants, both being su])jected to the same conditions which would have 

 influenced them had they remained in the held, except that the ants in 

 attendance were excluded. On May 8, 188«), corn was planted in these 

 cages and grew therein till after the loth of June — when it was thrown 

 out — without a single individual of either 

 root or aerial form of the root-aphis being 

 on or about the plants. 



Dr. S. A. Forbes, State entomologist of 

 Illinois, under whose direction most of the 

 investigations of these insects have been 

 carried out, in summing up the results of 

 a long series of carefull}' conducted experi- 

 ments of his own, comments as follows: 



Fig. 2.— The corn luaf-aphis (Aphis 

 mnidh): Winsloss female. Much 

 enlarged (original). 



The foregoing data confirm our ignorance more 

 than they increase our knowledge, showing, as they 

 do, the failure of all attempts to find or produce a 

 bisexual generation or an alternative food plant of 

 Aphis maidts, or to learn how and where it normally 



passes the winter. Its willingness to feed on winter wheat and ability to breed 

 freely on that plant, its indisposition toward grass or the foliage of the apple, and 

 the natural frequency of successive generations, are the princiiml other facts evident 

 from these ot)servations.« 



Winged females of the root-aphis occur in summer on the leaves of 

 corn together with those of the leaf -aphis, but never in such immense 

 numbers. The two forms of winged females seem to be distinguish- 

 able, but the sexes have never yet been observed to interbreed — 

 indeed without males above ground they could not do so; hence it is 

 yet too much to say whether there are two distinct species, with the 

 males of but one yet discovered, or whether these are two forms of a 

 single species, with as yet undiscovered relationships obscured by 

 long-continued influences of ants. As it is with the root-aphis that 

 the farmer has most to do, that species will be chiefly considered here. 



f Twent^'-third Report, State Entomologist of Illinois, p. 133, 1905. 



[Cir.SO] 



