February, '19] WOGLUM; LIQUID HYDROCYANIC ACID 117 



In the practice of rotation for the control of this species it is evident 

 that a change in the cropping system is hardly necessary more often 

 than once in five years. 



Where the area infested is small, it has been found practical to allow 

 hogs to run on the field temporarily. Hogs show a great preference for 

 white grubs, and will root to a depth of several inches to get them. 



Plowing immediately after harvest, and keeping the ground free from 

 all vegetation during the summer is always practical, since this proced- 

 ure will deprive most of the grubs and the adult beetles of food. The 

 keeping down of weeds around the edge of the field will also deprive 

 the adults of food. 



Literature Cited 



CocKERELL, T. D. A. Entomological Observations in 1894. New Mex. Agri. Exp. 

 Sta., Bui. 15, 1-82. 1895. 



Davis, J. J. A Progress Report on White Grub Investigations. Journ. Econ. Ent. 

 9:261-281. 1916. 



Forbes, S. A. A Monograph of Insect Injurious to Indian Corn, Fart I. Eight- 

 eenth Rept. State Ent., 111., pp. 1-171. 1894. 



Howard, L. O. Notes from Correspondence. Injury by Wingless Maybeetles in 

 Texas. U. S. D. A., Bur. Ent., Bui. 22 n. s., p. 107. 1900. 



Sanderson, E. D. Insects of 1903 in Texas. U. S. D. A., Bur. Ent., Bui. 46: 92-96. 

 1904. 



Miscellaneous Cotton Insects in Texas. U. S. D. A., Farmers Bui. 223: 



13-14. 1905. 



Report on Miscellaneous Cotton Insects in Texas. U. S. D. A., Bur. Ent., 



Bui. 57: 1-63. 1906. 

 Say, Thomas. Descriptions of Coleopterous Insects collected in the late Expedition 

 to the Rocky Mountains, performed by order of Mr. Calhoun, Secretary of War, 

 under the command of Major Long. Journ. Acad. Nat. Sci., Phila., 3: 238-282. 

 Leconte Edition 2: 142. 1824. 



RECENT RESULTS IN THE FUMIGATION OF CITRUS TREES 

 WITH LIQUID HYDROCYANIC ACID 



By R. S. WoGLUM, U. S. Department of Agriculture, Bureau of Entomology, 



Alhanibra, Cal. 



The fumigation of citrus trees with hydrocyanic acid gas has been 

 performed in California for more than thirty years and during this 

 period more radical changes in apparatus and methods have occurred 

 than is to be found in the annals of any other insecticide either in this 

 state or elsewhere. The original so-called "dry gas" process in which 

 undiluted sulphuric acid was poured slowly into a cyanid solution, the 

 resultant gas passing through a sulphuric acid bath, gave way in 1890 



