636 ANNUAL EEPORTS OF DEPARTMENT OF AGRICULTURE. 



the insect and the successful results obtained by sprays have resulted 

 in a very active interest on the part of orchardists themselves, and a 

 large number of power sprayers have been purchased and extensive 

 spraying operations begun under the advice and immediate super- 

 vision of agents of the Bureau. The total area of orange groves 

 treated for the orange thrips during the spring of 1910 is approxi- 

 mately 2,000 acres. . This is the more remarkable when it is remem- 

 bered that previous to the spring of 1909 practically no spraying 

 "whatever was practiced. 



INVESTIGATION OF HYDROCYANIC- ACID GAS FUMIGATION IN CALIFORNIA. 



The investigation of hydrocyanic-acid gas fumigation in Cali- 

 fornia, taken up at the beginning of the fiscal year ending June 

 30, 1908, was completed with the close of the fiscal year ending 

 June 30, 1910. The same character of field work has been continued 

 throughout, and efforts were made to conduct the investigation on as 

 nearly a commercial scale as possible, so that conditions and results 

 would be those normal to the ordinary care of citrus groves. The 

 results, which have been brought together in the form of a bulletin 

 about to be published, have been very satisfactory. The orange 

 growers expressed themselves as pleased, and the expense of the opera- 

 tion has been very considerably reduced, and, as a result of the 

 efficiency obtained, longer intervals between fumigations will now 

 serve to keep the groves in good condition. Important experiments 

 have been conducted with sodium cyanide, and it has been found 

 that with the use of a high-grade sodium cyanide the results are as 

 satisfactory as with a high-grade potassium cyanide. When it is 

 considered that the present manufacture of sodium cyanide is more 

 universal and greatly in excess of potassium cyanide ; that the sodium 

 compounds required in the manufacture of sodium cyanide are widely 

 distributed throughout the world, while commercial deposits of po- 

 tassium compounds required in the manufacture of potassium cyanide 

 are largely confined to the German Empire, and also that the present 

 unit price of sodium cyanide averages slightly less than that of the 

 other, it may reasonably be expected that in the future the sodium 

 may be found supplanting potassium in American usage. 



The field laboratory at "N^Hiittier, Cal., used in these investigations, 

 was abandoned June 30, when the lease expired, and the apparatus 

 was turned over to the Bureau. The agent in charge, Mr. R.. S. 

 Woglum, was transferred to another investigation. 



inat:stigations of insects in their direct relation to the health 



of man and domestic animals. 



One of the most interesting investigations under the branch of 

 the Bureau w^ork dealing with insects in their direct relation to the 

 health of man and domestic animals has already been mentioned in 

 this report in the earlier section on " "Work on the jointworm." As 

 the jointworm is a host of the mite in question, it is considered in full 

 in that section rather than here. 



The subject of remedies and preventive measures for mosquitoes 

 has been considered at great length in a bulletin published in the 

 spring of 1910 (No. 88), and the whole ground has been rather thor- 



