83 



fertilized or not, it was of course impossible to say. Another female 

 shut up in a petrie dish, August 26, 1905, deposited upon the glass 

 sixty eggs in chains within two minutes. 



The earHest date at which we have found the eggs in the field 

 is August 15, and the latest date at which we have seen them laid was 

 October 24, when a root-worm beetle deposited several eggs on the 

 side of a breeding-cage, two of them under the observation of the at- 

 tendant. Our additional data of life history are embodied in the ac- 

 companying diagram, from which they may be readily obtained, with- 

 out further description. 



Fig. 1. — Diagram of Life History of Diabrotica longicornis 



The Effect of Rotation of Crops on Injury by the Corn Root- 

 Worm. — It has long been known that the standard method for the pre- 

 vention of corn root-worm injury, quite certain in its effect, is rotation 

 of crops. The eggs being laid mainly, if not altogether, in old corn- 

 fields, and most plentifully in those which have been previously in- 

 fested, and the larvae which hatch from these eggs the next spring living 

 only on the roots of corn, it necessarily follows that if corn is planted 

 on ground not in corn the previous year it can not be injured by root- 

 worms. In order to get more definite information upon this subject, 

 and especially to show the maximum number of years within which it 

 is safe to continue corn on the same ground, data of infestation as re- 

 lated to length of time in corn were collected for me in 1904 by Mr. E. 

 P. Taylor, then an assistant in my office. The fields visited were taken 

 at random in Ford and McLean counties, in neighborhoods to which 

 our attention had been called by complaints and inquiries with regard 

 to this insect. 



For this purpose seventy-one fields were carefully examined, and 

 an estimate was made of the percentage of the hills obviously affected 



