67 



account can be taken in this discussion, since the beetles of this genus 

 do not feed on the leaves of trees. 



One hundred miles of additional travel behind the plow in 1909 — 

 77.5 miles in Kane county and 22.5 miles in Marion and Perry coun- 

 ties — proved on analysis to have been done in localities where white- 

 grubs were so few that the data of that year could not be used in this 

 discussion. The northern Illinois fields averaged only eight grubs to 

 the mile, instead of the average of twenty-eight to the mile of the 

 earlier collections, and most of these fields yielded only one or none in 

 the same distance. The southern Illinois fields, altho practically sur- 

 rounded by woodlands and orchards, gave us only twelve grubs to the 

 mile in 1909, and lacked the contrast of surrounding conditions nec- 

 essary to the inquiry. 



For purposes of classification, my data sheets were assorted into 

 four groups, according to the distances of the fields from the nearest 

 trees — group 1 relating to fields with trees within or on their borders 

 or within less than an eighth of a mile; group 2, to those with trees 

 more than an eighth but less than a fourth of a mile away ; group 3. 

 to those with trees more than a quarter of a mile away and less than 

 a half ; and group 4. to those with trees half a mile away or more. Two 

 hundred and twenty-four miles were traveled in fields belonging 

 under group 1, with the result that white-grubs of the genus Pliyllopli- 

 aga were found at an average rate of 39.17 to the mile; forty miles 

 were traveled in fields of group 2. and in these Phyllophaga grubs aver- 

 aged 17.83 to the mile ; in fields of group 3, a hundred and thirty miles 

 were traveled, and Phyllophaga grubs averaged 15.94 to the mile ; while 

 in group 4, thirty-five miles were traveled, giving 14.4 as the average 

 number of Phyllophaga grubs. From this it would appear that fields 

 so situated with reference to fruit, shade, or forest trees that May- 

 beetles might feed within them, on their borders, or within less than 

 an eighth of a mile away, contained two and a fifth times as many 

 white-grubs as those whose nearest trees were between an eighth and 

 a quarter of a mile distant; that they contained practically two and 

 a half times as many grubs as those whose nearest trees were between 

 a quarter and a half mile away; and that they contained two and 

 three quarters times as many grubs as those with trees half a mile 

 away or more. 



No attempt was made, in collating these data, to distinguish be- 

 tween the different kinds of trees — a useless task, as the different 

 species of beetles have different preferences as to food: and it is im- 

 possible to separate the grubs by species. Ample materials on this 

 subject are contained in the paper entitled "A General Survey of the 

 May-beetles (Phyllophaga) of Illinois," immediately preceding. 



The Kinds of Crops in which May-beetles Prefer to lay their 

 Eggs. — The information derived from these collections has enabled me 



