2 BULLETIN" 218, TJ. S. DEPARTMENT OF AGEICULTUEE. 



first few experiments showed that many of these were of little value 

 as stomach poisons, their use was discontinued. 



A few homemade preparations were tested in the course of these 

 experiments. Those used in 1912 were arsenate of iron, arsenate of 

 zinc, and arsenite of lime. The methods of preparation of these ma- 

 terials were as follows: 



Arsenate of iron was prepared hy dissolving 4 pounds of sodium- 

 arsenate crystals and 4 pounds of iron sulphate each in 2 gallons of 

 hot water. The iron-sulphate solution was then poured slowly into the 

 sodium-arsenate solution, the solution being stirred vigorously at the 

 same time. Arsenate of iron was used at a rate equal to O.S pound of 

 sodium arsenate to 50 gallons of water for the ordinary strength. 



The arsenate of zinc (homemade) was prepared in the same way 

 as arsenate of iron, sodium arsenate and zinc sulphate being used, 

 and the strength being based upon the sodium-arsenate content, the 

 same as for arsenate of iron. 



Arsenite of lime was prepared by boiling 2 pounds of white arsenic 

 and 2 pounds of sal soda in 1£ gallons of water until thoroughly dis- 

 solved, and this was used to slake 4 pounds of stone lime. After 

 slaking, enough water was added to bring the total to 2 gallons. This 

 was used at the rate of 2 pints to 50 gallons of water, which is 

 equivalent to one-fourth pound of white arsenic to 50 gallons of water. 



LABORATORY TESTS. 



During the season of 1912 the fall web worm (HypTiantria cunea 

 Drury) was used for all the experiments, since this insect could be 

 readily obtained in large numbers, and proved to be an ideal species 

 for handling in the laboratory. Very young larva?, usually 3 or 4 

 days old, were used in all the tests. The larvae were fed with foliage 

 of the wild black cherry (Prunus serotina), which was foimd to be a 

 favorite food plant of the fall webworm in Michigan. Twigs having 

 from 20 to 30 leaves each were sprayed by means of a large atomizer 

 of the type in which quart jars are used as a container for the liquid, 

 and the stems of the twigs were placed in small glass jars containing 

 water. 



After the spray had thoroughly dried, allowing from 6 to 12 hours, 

 20 insects were placed on the leaves of each twig. A large paper bag 

 was then placed over the twig and held to the glass by means of a 

 rubber band to prevent the escape of the larva?. At each examina- 

 tion the bag was removed and the dead larva? taken out and counted. 

 When all the insects were dead or had pupated, as the case might be, 

 the amount of foliage consumed was measured in square inches. A 

 sheet of celluloid, cross-sectioned to 0.01 of a square inch, was util- 

 ized for this purpose. These measurements were easily taken where 

 effective poisons were used, as the young larva? died before very 



