54: 



tance from woodlands, by driving the adult chinch bugs from the 

 open fields and compelling them to resort to the grassy woods for 

 food for themselves and their young. 



Severe drouth in a small-grain district has so thoroughly and 

 so early destroyed the corn crop there, as to test practically the 

 efiPect of abandoning that crop as a defence against the chinch bug. 

 In the case observed, it was found that the injury the following 

 season was very much less than before. As the drouth took effect, 

 however, on the field grasses generally, and thus still further re- 

 duced the supply of insect food, the result was not to be attrib- 

 uted wholly to a lack of corn. 



A similar destruction of the corn by drouth in midsummer fol- 

 lowed by a general winter- killing of wheat, has shown that a suc- 

 cessive abandonment of these crops may greatly reduce the num- 

 bers of the chinch bug, even where other conditions are very 

 favorable to it, this reduction amounting, in one such case, to one- 

 half or three fourths of the number abroad the year preceding. 



Where wheat is abundant in a district very badly infested by 

 chinch bugs, it is now certain that this insect may live and breed 

 very successfully in early spring in oats, in young timothy and 

 blue grass meadows, and even in corn. 



A thorough-going investigation of the relations of chinch-bug 

 injury to the acreage of the principal farm crops of Illinois in 

 1886 and 1887 shows that, where the outbreak was but just begin- 

 ning, the wheat area had evidently much to do with the number 

 and the rate of increase of the insects, a rising gradation of 

 injury appearing in correspondence to an enlarging area in wheats 

 the acreage of the other crops at the same time remaining 

 nearly constant or slightly declining. As the severity of the 

 attack increases, however, the oats area begins to rise with the 

 wheat, and may presently surpass the latter as a stimulus to the multi- 

 plication of the chinch bug, corn and grass finally showing a like 

 tendency where it has become excessively abundant and destruct- 

 ive. Here, when the eggs of the winter brood are being laid freely 

 on all the food plants of the species, the wheat area may even 

 decline as one passes from districts where destruction is very great 

 to those in which it is complete. This may be due to one or 

 more of the following circumstances: (1.) The wheat area may be 

 purposely diminished by the farmers, one year after another, as 

 was certainly sometimes the case in southern Illinois in 1887, 

 where chinch-lnig injury had greatly lessened the yield and value 

 of the crop for the season or two preceding; (2.) A change of 

 feeding ha])its nifiy arise among the insects themselves;* or (3.) 

 there may be ii spontaneous gradual shifting of the center of at- 

 tack, due to a natural diminution in the number of insects one 



•Hnch viirljitloiiH In (:hol(;« f>f food undor dlffonrnt conditlonH aro not by any means rare among 

 InHoctH. Tlu< lI<!KHian (ly, for fxuiiiiilc. Ih vnry dt^Htnu ti vo to ryo In Europo, wlillo hero it is alniost 

 nov<rr Hci-u In tliat Rriiin; and the rldndi huR Itwlf lian niado In Now \ork a severe attat-k on 

 niea(]o\vH wlilh; not n<it i< i'al)ly liuniihiK any ccroal crop. 



