4 BULLETIlsr 796, U. S. DEPARTMENT OF AGRICULTUEE. 



Carbon Tetkachloeid. 



Carbon tetrachlorid does not differ essentially from carbon di- 

 siilphid, in so far as its effect upon the tree or its larvicidal action 

 is concerned. To achieve the same result it seemed to require about 

 double the dosage of the disulphid. Its chief merit as a fumigant 

 seems to lie in the fact that the vapor is not inflammable. 



Naphthalene. 



Naphthalene was tested quite fully in 1916 and 1917. For the 

 greater part of the year it vaporized just fast enough to give the 

 soil about the base of the tree a pronounced odor, but apparently 

 produced no effect upon the insect or the tree. With a soil tempera- 

 ture of 70° F. and over, attained in July and August, there is a very 

 decided larvicidal action, but not sufficient to make this material of 

 value. 



Hydkocyanic-acid Gas. 



Hydrocyanic-acid gas, while a very effective larvicide, proved too 

 dangerous. The great solubility of this gas effectually prevents the 

 standardization of its use. Variation in moisture content and in the 

 type of soil so greatly affect the absorption of this gas b}^ the latter 

 that it has been found impossible to establish any standard dosage 

 that is both effective and safe for any number of conditions. Moist 

 soils required much larger doses than dry soils or soils of low water- 

 holding content. This point has been fully covered by Ong^ in a 

 recent publication. The great solubility of the gas, furthermore, 

 leads to its rapid absorption by the portions of the tree with which 

 it comes in contact, which probably explains in part the considerable 

 injury resulting from its use. 



PARA-DICHLOROBENZENE. 



Insecticidal, Physical, and Chemical Pkopeeties. 



Of ithe various volatile compounds tested, the merits of some of 

 Avhich have been briefly discussed, para-dichlorobenzene has been by 

 far the most promising. While well known chemically, its value as 

 an insecticide is of comparatively recent discovery. 



Of the various volatile compounds tested, the merits of some of 

 which have been briefly discussed, para-dichlorobenzene has been by 

 far the most promising. Wliile well known chemically, its value as 

 an insecticide is of comparatively recent discovery. Duckett,^ in 

 1915, published a report on the insecticidal value of its vapor as a 

 fumigant against various insects. Later in the same year Cook, 



1 Ong, B. R. de. Htdrocyaxic-acid gas as a soil fujiigant. In Jour. Agr. Research, 

 V. 11, no. 9, p, 421-436. 1917. 



2 DucKETTj A. B. Para-dichloeobenzene as an insect fumigant. U. S. Dept. Agr. 

 Bui, 167. 1915. 



