49 



two years without a change to some crop on which the root-lice can 

 not live; and the other, a deep plowing and repeated deep stirring of 

 infested corn-fields before they are planted to the next year's crop, so 

 timed and managed as to break up the nests of the ants and to scatter 

 their contents — their delicate eggs and larvae, and the eggs and young 

 of the root-lice — so thoroly that these will be lost to their attendant 

 nurses and protectors and will perish for lack of care and food. 



Several attempts were made by us, additional to those already 

 published, to test the effect and value of this deep cultivation method, 

 and we had one excellent opportunity to observe accurately the effect 

 of a change of crop. 



Cultivation Experiments at Bloomington 



In July, 1909, a field of five acres near Bloomington, 111., already 

 in corn and heavily infested with ants and root-lice, was rented for our 

 use and was plowed for replanting July 9, 10, and 12. It was my pur- 

 pose in the main experiment to test the effect on the ants and aphids 

 of certain variations in the preparation of the ground for corn. The 

 principal part of the field rented was divided into five plots, each five 

 rods wide by twenty rods long, and each plot was separately plowed, 

 with an unplowed strip from three to five feet left between it and the 

 plot next to it. Our object in leaving these unplowed strips was to 

 provide an undisturbed place of retreat for the ants which would en- 

 able the observers to detect and trace the escape of the colonies if our 

 operations had the eft'ect to drive them out of the experimental plots. 

 The ])low was followed in each of these plots, with the result that 

 113 ants' nests were seen in 500 rods of furrow. This is at the rate of 

 72 1/3 nests to the mile of furrow fourteen inches wide, a number 

 equivalent to 512 nests to the acre. 



Owing to the fact that the field was already in young corn, these 

 data of infestation obtained by counting the nests broken into and 

 turned out when the ground was plowed in July are hardly compar- 

 able with those obtained during the first spring plowing of other fields. 

 In spring the ants are concentrated in their hibernating colonies, but 

 these family groups become considerably subdivided among the corn 

 hills after the corn has begun to grow. 



All the experimental plots, Nos. 2-5, were plowed as nearly as 

 possible to a depth of six inches. The check plot. No. 1, was plowed to 

 a depth of four inches, then harrowed twice with a toothed harrow 

 working about two and a half inches deep, and planted on the 22d of 

 July. Plot No. 2 was disked three times — July 13, 16, and 19 — with a 



