No. 509] 



ECOLOGY OF INDIAN CORN PLANT 



295 



ever, that when the life history of a food plant, or the 

 common history of a group of such plants, exhibits suffi- 

 ciently constant characters to serve as an adaptive matrix, 

 an adaptation to it of the life history of those insects 

 strictly or mainly dependent on it for food is more or less 

 likely to follow. 



Mutual Biographical Adjustments of Competitobs 

 An example of the competitive relations into which corn 

 insects of widely different character, origin, habit and 

 life history may be brought by their dependence on the 

 same food plant may be found in Diabrotica longicornis 

 and Aphis maidiradicis. Both pass the winter as eggs in 

 the earth of the corn field, the aphis hatching sooner than 

 the root-worm, and developing two or more of its short- 

 lived generations before the Diabrotica larva is out of the 

 egg, gaining thus the advantage of an earlier attack m 

 greater numbers. It is also able to take much more 

 rapid possession of a field of corn because of its command 

 of the services of ants in finding its way to the roots of 

 the plants which the tiny and feeble Diabrotica Larva 

 must search out for itself. 



Later the root-aphis gives origin to young, many o 

 which acquire wings and may thus disperse as their local 

 attack upon the plant becomes unduly heavy, while the 

 root-worm must take its chances for the year m the held 

 where the eggs were left the previous fall. ' ^ 

 feeds at first on the sap of young weeds common in >i>i mir 

 in all cultivated fields, and may thus save itselt ^e\en 

 though the ground is planted to wheat <>r oat-, an »^\< n 

 which causes the death by starvation of every ro 

 hatching from the egg. his has 



In respect to rate of multiplication, the r0 ° ^'J^ Jj^j 

 of course, a truly enormous advantage as com ^ u jj ( 

 the corn root-worm, and yet, notwithstam ing a 

 facts favorable to the aphis, it- injuru-s to ,-orn in ^ 

 are seemingly no greater than those done > 

 root-worm. This is due partly to the fact that, through 



