THE INFLUENCE OF TREES AND CROPS 

 ON INJURY BY WHITE-GRUBS 



By STEPHEN A. FORBES, State Entomologist 



White-grubs most abundant in tlie Xeigliborlwod of Trees. — The 

 fact that our common May-beetles, the parents of most of our white- 

 grubs, fly back and forth each morning and evening between the trees 

 upon which they feed at night and the ground on which they hide by 

 day and in which they lay their eggs, and the further fact that they 

 are never seen to move long distances from place to place, lead to the 

 natural supposition that fields nearest to their food-plants must be- 

 come most heavily stocked with eggs, and consequently worst injured 

 by grubs when these eggs have hatched. It has, in fact, been fre- 

 quently noticed that this seems to be the case ; and it was for the pur- 

 pose of getting definite information on the subject, in a form for state- 

 ment in ratios of frequency or degrees of injury, that I began in 1904 

 to instruct my field assistants to make collections of white-grubs from 

 fields which were being plowed either in fall or spring. For this pur- 

 pose they walked behind the plowman, making note of the distance 

 which they traveled in each field, counting the grubs exposed by the 

 plow, and recording at the same time the distance from the field to the 

 nearest trees upon which the May-beetles, the parents of the white- 

 grubs, might be supposed to have fed. Their data concerning abun- 

 dance of the grubs were recorded in the form of numbers per mile of 

 furrow traveled. The data sheets gave also the locality and date of 

 each collection, the name of the owner of the field, the crop of the 

 year and of the four years immediately preceding, the character and 

 classification of the soil, its level — whether upland or lowland — its 

 condition as to drainage, and the kinds of trees in the neighborhood, 

 as well as the distance of these trees from the margins of the field. 

 Observations and collections of this sort were continued by six of my 

 field assistants as opportunity offered, during the years 1904, 1905, 

 1907, and 1908. In this time white-grubs were collected from five 

 hundred and forty-nine fields widely scattered thruout central Illinois, 

 with a few fields also in the northern and southern parts of the state. 

 The total distance traveled in this pursuit was a trifle over four hun- 

 dred and twenty-nine miles, and the total number of grubs of the 

 genus PJiyllopliaga obtained was 12,069. In addition to these, 1187 

 grubs of the genus Cyelocepliala were collected, of which, however, no 



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