BUREAU OF ENTOMOLOGY. 229 



atmospheric pressure. The initial experiments were conducted in a 

 small fumigation chamber, 36 inches long by 12 inches in diameter. 

 By the use of this chamber a number of different kinds of seeds and 

 insects were fumigated successfully under a reduced pressure. In 

 addition to the fumigation of seed, many tests were made with 

 various deciduous plants, resulting in perfect control of the insects 

 without injury to the buds. 



In order further to test the penetration of hydrocyanic-acid gas 

 in the presence of a partial vacuum, some 40 bales of Chinese, Peru- 

 vian, and Egyptian cotton were fumigated in a chamber containing 

 98 cubic feet. To determine the effect of the gas on insects at 

 various points in these bales, steel tubes drawn to a point at one end, 

 with small perforations at the small end, were driven into the bales 

 to various depths. The insects were then suspended in these tubes 

 in glass vials plugged with cotton, and the ends of the tubes extend- 

 ing outside of the bale were either sealed with a lead screw cap or 

 with a rubber stopper sealed with glycerin. Under these unusual 

 conditions it was lound possible to destroy the larvse and adults of 

 the confused flour beetle and the rice weevil and larvse of the bean 

 weevil and the common clothes moth. The experiments conducted 

 during the past year definitely proved that the efTiciency of hydro- 

 cyanic-acid gas is greatly improved in the presence of a partial 

 vacuum, and that this efficiency increases as we approach a perfect 

 vacuum. The work gives a practicable method of control of certain 

 insects which have hitherto been beyond reach, and wiU assist in a 

 very important way m preventing the introduction of new pests. 



Citrous-fruit insects in California. — The investigation of the 

 citrous mealy bug, begun during the preceding year, was continued. 

 In the hfe-history studies and methods of control satisfactory progress 

 was made. Incidentally, various parasitic and predaceous enemies 

 of these destructive insects were under observation. 



Experimental work to determine the agencies responsible for fruit 

 injury during the process of fumigating citrous trees with hydro- 

 cyanic-acid gas was carried on and definite data on this subject 

 have been secured. 



Citrous-fruit insects in Florida. — The investigations of insects 

 affecting citrous fruit trees in Florida were continued, for the most 

 part, along the hues indicated in the last annual report. It has 

 been conclusively demonstrated that by the proper use of sprays 

 the fruit output can be greatly increased and the quahty much 

 improved. 



Citrous-fruit insects in Louisiana. — The investigations of 

 insects affecting citrous fruit trees in Louisiana progressed very 

 satisfactorily. The Argentine ant was the subject of special investi- 

 gations, and much information was gained on the amount of iniiu-y 

 occasioned by this insect to citrous trees, and the possible methods of 

 control. Methods of controlling the chaff scale and citrous white 

 fly were also under consideration. Considerable information was 

 secured on the biology of the fig borer, which at times occasions 

 considerable injury to the fig trees. 



Insects affecting date palms. — The investigation of date-palm 

 insects was brought to a conclusion in December, 1914, and the 



