148 ANNUAL REPORTS OF DEPARTMENT OF AGRICULTURE. 



to the north and to the east, and appeared to threaten great danger 

 to this vitall}^ important crop of the irrigated regions of the West. 

 The bureau's experts have been studying it since the beginning, 

 have been engaged in importing its natural enemies from Europe 

 (it is a European insect), and have now discovered a method by which 

 the pest ean be handled after the first crop of alfalfa has been har- 

 vested. It is hoped that in time some other means will be discovered 

 wherebj' the important first crop can be saved. 



INSECTS AS CAItRIERS OF DISEASES. 



Throughout the entire 16 years the important subject of the car- 

 riage of diseases of man and animals by insects has been investi- 

 gated. The mosquitoes that carry malaria and yellow fever have 

 been carefully studied, and publications have been issued warning 

 people and giving remedies. 



In the same way the relation of the common house fly to the car- 

 riage of typhoid fever and other intestinal diseases has been studied, 

 and in the same way publications of warning have been issued, and 

 these have given remedies. 



The tick which carries the Rocky Mountain spotted fever has also 

 been studied, and an investigation has been completed which points 

 out a way to control this dangerous creature. 



The ticks that carry the Texas fever of cattle have also been 

 made the subject of intensive study, and many facts have been 

 ascertained Avhich are of service to the Bureau of Animal Industry 

 in its large-scale work in pushing the quarantine line against south- 

 ern cattle farther and farther to the south. 



FUMIGATING CITRUS TREES. 



The process of fumigating citrus trees with hydrocyanic-acid gas, 

 which was carried on at a very great expense by the prosperous own- 

 ers of citrus groves in southern California a few years ago, has been 

 studied with the utmost care, and as a result the expense of the 

 process has been reduced to a, remarkable degree. A single grower 

 has stated that the result of this work has saved him a quarter of a 

 million dollars. 



INSECTS INJURIOUS TO TREES. 



Facts determined within the past 10 years indicate quite conclu- 

 sively that 7 species of bark beetles of the genus Dendroctonus. 

 injurious to coniferous trees, have killed more merchantable pine, 

 spruce, and Douglas fir timber in this country than has been killed 

 in the same period by forest fires. Investigations by the bureau have 

 resulted in the gaining of a very complete knowledge of these injuri- 

 ous species and in ascertaining methods of control. The success of 



