105 



renew it only when the odor became too faint to repel the bugs. On 

 this account it was only necessary to prepare a fairly level strip on 

 which it might be poured, careful smoothing and firming of the path 

 being unessential. 



That it is the odorous vapor of creosote which prevents the pas- 

 sage of the bugs is illustrated not only by our field observations of the 

 reluctance of the insects to approach the creosote strip, but also by an 

 experiment made by Mr. Flint at Springfield in December, 1913. 

 Fifty adult chinch-bugs were confined in an open box, 19x9 inches and 

 iy 2 inches deep, by chalking the upper edges of the sides. After they 

 had settled quietly, various strong-smelling substances were introduced 

 among them. Tested in this way the chinch-bugs paid no attention to 

 sulphur or asafetida, and but little to wood soaked with chlorhydric 

 acid, but they immediately scattered when exposed to the vapors of 

 creosote, none of them coming within two inches of the object for 

 the next four hours during which they were watched, and still keep- 

 ing at a distance of an inch from it five hours later. Formic acid 

 was almost equally repellant. 



Altho a creosote line was not so complete a protection as one of road 

 oil, a small percentage of the chinch-bugs filtering past it even when 

 it was properly laid and carefully supervised, yet the number was 

 never large enough to do noticeable harm to corn ; while in one respect 

 the creosote barrier was better than the road oils since its odor was 

 not affected by dust, straws, or other rubbish blown across it, such as 

 would often cover or bridge a road oil line in a way to allow the bugs 

 to pass it readily. The efficiency of an old creosote barrier might even 

 be increased by a shower of rain sufficient to destroy that of a road- 

 oil line by washing parts of it away or covering them with dirt. The 

 creosote, being lighter than water, rose to the surface when the ground 

 was wet, and its efficiency was thus increased, rather than lessened, 

 by the rain. 



The average cost of the creosote used to keep up an effective bar- 

 rier during the chinch-bug migration season of 1914 was $16.50 for 

 each mile of the line. We have definite information of the use of 

 1840 barrels this year, at a usual cost of $7 to $10 a barrel according 

 to quantity and quality ordered. 



Experiments with Insecticide Sprays 



Kerosene Emulsion. — As a secondary method of defense against 

 chinch-bugs, very useful under certain conditions and in certain 

 emergencies, spraying with insecticides which kill by contact is es- 

 pecially to be advised. That a 5-percent kerosene emulsion will kill the 

 chinch-bugs at a reasonable expense was a fact first established by the 

 writer in 1882 ; but this material has the disadvantage that its correct 

 preparation requires special care and considerable labor, and that if 

 used on young corn it must be so applied as not to lodge in the ' ' heart 



