36 ASSOCIATION OF ECONOMIC ENTOMOLOGISTS. 



In the uninfestecl field 2,000 hills bore 4,024 ears, 201 of which were 

 small; hi the infested field 2,000 hills yielded a total crop of 95 ears, 

 all nubbins. Sixty-eight per cent of the hills in the first field were 

 still infested by ants and 67 per cent by aphides, while 69 per cent 

 of the vacant hills, in which the corn had died, still showed by the 

 presence of old ant burrows, now deserted, the cause of their death. 

 In brief, the one field yielded an excellent crop of corn and the other 

 was wholly ruined by the root-aphis alone, yielding neither fodder 

 nor grain worth taking into account. 



This was no isolated instance; it was simply a strongly marked 

 example of aphis injury in that neighborhood, wherever corn had 

 grown on the same ground for so little as two years in succession. 

 The corn root-aphis has simply become epidemic there. Winged 

 females swarm out of the older fields in late spring and early summer 

 in such overwhelming numbers that any field is likely to be injured 

 by them and to become so heavily infested that aphis eggs enough 

 will be left in the ground in fall to work the complete destruc- 

 tion of the crop the following year if the ground is planted to corn. 

 One year at a time in corn is about the limit under such conditions. 

 Whether even so prompt rotation as that would hold this ant-aphis 

 pest permanently in check will appear from what I shall presently 

 have to say concerning the fate of the aphis if the ground containing 

 its eggs is planted to some other crop than corn. 



Furthermore, I regret to say that this Ford County neighborhood 

 is only one of several known to me in various parts of Illinois which 

 are similarly injured and endangered. It is because the conditions 

 here described may become established anywhere that corn is made 

 continuously the leading crop that I have thought my topic an 

 especially appropriate one for this general meeting of the American 

 economic entomologists. 



NATURAL CHECKS ON INCREASE. 



The possibilities of serious permanent injury to corn culture by 

 the root-aphis are greatly increased by the fact that these subter- 

 ranean aphides, while in no way inferior in reproductive capacity 

 to species of aerial habit, are not nearly so subject to rapid whole- 

 sale destruction by rains, or by parasites and other insect enemies. 

 Long-continued or oft-repeated rains sometimes retard their multi- 

 plication, it is true, and may even reduce their numbers somewhat, 

 but no changes of weather have any such effect on them as on the 

 grain aphides, for example. While the corn leaf-aphis (Aphis mai- 

 dis Fitch) is enormously parasitized, and is commonly attacked by 

 the usual kinds of aphidivorous insects, Aphis maidi-radicis is never 

 parasitized, so far as I know, and it is but little subject to destruction 

 by other insects underground. 



