476 Bulletin No. 116. lAugust, 



Relation to Soii, and Subsoil. 



It is a matter of common opinion that-injuries" by white-grubs 

 are more serious on the higher, hghter, and drier parts of our culti- 

 vated areas than on the lower and moister parts, but no exact ob- 

 sevations have been made to show whether this apparent difference 

 is real under all conditions, and whether, if so, it is due to a greater 

 abundance of the grubs on high lands than on low, or to a lesser 

 average power of recuperation and resistance on the part of plants 

 growing in comparatively light and less fertile soils. 



I began in 1904 and 1905 to accumulate data on this and allied 

 points, by having collections of white-grubs made by persons follow- 

 ing the plow, who recorded for each field and situation the numbe£_ 

 of grubs found in each quarter of a mile of furrow. A record was 

 also made, for each field examined, of the succession of crops it had 

 borne for the five years preceding, of the character of the soil, the 

 lay of the land, the conditions as to drainage and to fertilization, 

 and the relation of the field to trees and shrubs on which the parent 

 beetles of the grubs might have found food. Collections were made 

 on this plan from seventy-nine fields in the following twelve counties 

 of central and southern Illinois: Stark, Peoria, Woodford, Mc- 

 Lean, Champaign, Macon, Macoupin, St. Clair, Washington, Ma- 

 rion; Jackson, and Union. This work was interrupted by lack of 

 funds and by diversion of assistants to more pressing problems 

 before any sufficient mass of data had been obtained to enable me 

 to draw satisfactory general conclusions on any one of the points of 

 principal interest. So far as they go, they show that the grubs were 

 more abundant on the higher and drier parts of the country than on 

 the lower and moister parts, and that the fewest eggs were laid by 

 the parent beetles in corn fields and the most in grass-lands. Thirty- 

 eight low-land fields gave an average of 21 grubs- exposed in a mile 

 of plowed furrow, and 41 of the high-land fields an average of 31 to 

 the mile. The three largest numbers found in any fields were 208, 

 164, and 140 grubs to the mile, all on high ground. The largest num- 

 bers in any of the low.-land fields were 112 and 104 in two of them. 

 Again, the average of fields which had been in com continuously for 

 at least three years preceding was 17 grubs exposed in each mile of 

 furrow, and that of fields which, although in com at the time, had 

 -been in grass for several years preceding, was 37 gmbs to the mile. 

 It is evident that useful information may be obtained from data of 

 this description if they are accumulated in sufficient number and are 

 properly classified. 



