382 EEPORT UNITED STATES ENTOMOLOGICAL COMMISSION. 



sideriug tbe diiferent available destructive agents, coal-oil is the very 

 best and cheapest that can be used against the locusts. It may be used 

 in any of its cruder forms, and various contrivances have been employed 

 to facilitate its practical application. The main idea embodied in these 

 contrivances is that of a shallow receptacle of any convenient size (vary- 

 ing from about 3 feet square to about 8 or 10 by 2 or 3 feet), provided 

 with bigh back and sides, either mounted upon wheels or runners, or 

 carried (by means of suitable handles or supporting-rods) by hand. If 

 the '' pan " is larger than, say, 3 feet square, it is provided with trans- 

 verse partitions which serve to prevent any slopping of the contents 

 (in case water and oil are used), when the device is subjected to any sud- 

 den irregular motion,^such as tipping, or in case of a wheeled pan, when 

 it passes over uneven ground. The wheeled pan is pushed like a wheel- 

 barrow ; the hand- worked pan is carriexl by long handles at its ends. 

 On pushing or carrying, as the case may be, these pans, supplied with 

 oil, over the infested fields, and manipulating the shafts or handles so 

 as to elevate or depress the front edge of the pan as may be desired, the 

 locusts are startled from their places and spring into the tar or oil, when 

 they are either entangled by the tar and die slowly, or, coming in con- 

 tact with the more active portion of the oil expire almost immediately. 

 In Colorado they use it to good advantage on the water in their irrigat- 

 ing-ditches, and it may be used anywhere in pans or in saturated cloths, 

 stretched on frames, drawn over the field. The method of using it on 

 the irrigating-ditches in Colorado is thus reported by Prof. E. L. Pack- 

 ard : " It consists essentially in pouring, or, better, dropping coal-tar or 

 coal-oil on the running water with which the irrigating ditches are sup- 

 plied. The method of supplying these ditches with oil is very simple. 

 It is only necessary to sprinkle a few drops of coal-tar on the stream, 

 when the oils contained in the tar are diffused over the surface of the 

 water, and coming in contact with the insects (no matter how many), 

 cause their speedy death. The toxic power of coal-oil upon thd insects 

 is very remarkable; a single drop of it floating on the water is capable 

 of causing the death of a large number of insects. A simple and in- 

 genious mode of keeping up a constant supply of the tar to a ditch I 

 saw exemplified upon the farm of Mr. Arnett. A three-quart can is 

 perforated on the side close to the bottom, a chip loosely fitting the 

 aperture is inserted therein, and the can is then immersed (by a weight 

 if necessary) in the ditch. Three quarts or less of tar, trickling out 

 drop by drop from this slight vent, are sufficient to keep a great length 

 of ditch supplied with coal-oil for thirty-six hours. The precise extent 

 of ditch which may thus be rendered toxic to the locusts cannot, of 

 course, be exactly stated. It is in fact quite indefinite, for the reason 

 -that the quantity of oil necessary to kill one of the insects is almost in- 

 finitesimal, and for the further reason that a single drop of oil will cover 

 quite a large surface when dropped on water, so that taking these two 

 facts together, it is easy to see that a very small quantity of tar or oil 



