6a 



to distinguish also between the different kinds of crops with reference 

 to the preferences of May-beetles in searching for places to lay their 

 eggs. It has been well established, mainly by the breeding-cage work 

 of John J. Davis, of the U. S. Bureau of Entomology, that our most 

 abundant May-beetles have a three-year life cycle in Illinois. From 

 eggs laid by the beetles in spring or summer, grubs hatch the same 

 season, and then pass thru practically two entire years in the larval 

 or grub stage, and pupate in the third summer or fall after the eggs 

 were deposited. From these pupae the beetles are formed under- 

 ground, where they pass the winter, coming out at the end of the third 

 full year to lay their eggs. 



From this outline it is evident that white-grubs fairly well grown 

 in fall are from eggs deposited the year before, and that if one knows 

 the crop on the field that year he may say with confidence that the 

 parent beetles laid their eggs in that crop. Well-grown grubs seen 

 in spring and early summer, on the other hand, may have come from 

 eggs laid either the preceding year or a year still earlier. To be sure, 

 consequently, of the crop in which the eggs which gave origin to these 

 spring grubs were laid, we must know what crops the field has borne 

 for the two preceding years, and can make use only of those fields in 

 which the crops have been the same both years. If such a field has 

 been in corn, for example, for the last two years before the time of 

 observation, it is certain that the parent beetles of the spring white- 

 grubs must have laid their eggs in corn, whatever the age of the grubs. 

 By classifying my data sheets in accordance with these facts, I deter- 

 mined positively the crops in which the eggs were laid that had pro- 

 duced 9664 of our white-grubs, obtained during two hundred and 

 ninety-one miles of travel behind the plow. The following table shows, 

 for each crop in which May-beetles had laid their eggs, the number of 

 miles which my collectors traveled in making their collections, the 

 total number of grubs obtained, and the number per mile. 



Table showing Crops in which Eggs must have been Laid from which White- 

 grubs COLLECTED WERE HATCHED, TOGETHER WITH THE WHOLE NUMBER 



of Grubs collected, and the Number per Mile for each 

 such Crop 



Crop on ground when 





Number of grubs 



Number of grubs 



eggs were laid 





collected 



per mile 



Com 



177.1 



4342 



24.5 



Meadow crops, 









excluding clover 



37.5 



542 



14.7 



Pasture 



23.5 



1991 



84.3 



Wheat 



20.5 



1272 



62. 



Fallow ground 



18.5 



812 



43.3 



Oats 



9.38 



571 



60.9 



Clover 



4.5 



134 



29.7 





290.98 



9664 





