320 JOURNAL OF ECONOMIC ENTOMOLOGY [Vol. It 
bisulphide in warehouses might be overcome by having a special room 
constructed outside the warehouse. 
R. W. Doane: I recommended such a course in the case of a ware¬ 
house I visited a few days ago. 
President G. P. Weldon: The next paper in order is “Fumiga¬ 
tion Experiments: The Time Factor,” by A. F. Swain. 
FUMIGATION EXPERIMENTS: THE TIME FACTOR 
By A. F. Swain, University of California, Citrus Experiment Station, Riverside,, 
California 
Introduction 
The control of the insect pests of citrus trees in California is accom¬ 
plished largely by the use of hydrocyanic acid gas. As practiced at the 
present time, there is a considerable variety in the methods of proce¬ 
dure, and th6re are many problems on which further data are desirable. 
Among these is the determination of the proper time of exposure; 
whether the times in most common use, namely, 45 and 60 minutes, 
are the most practical; whether a shorter period would suffice or a 
longer period be more efficient; and whether there is any real differ¬ 
ence in the efficiency between the 45 and 60 minute periods. 
While carrying on some fumigation experiments for another purpose 
during the season of 1916-1917, the writer was impressed by the fact 
that there did not seem to be any constant and appreciable difference 
between exposures of 45, 50, and 60 minutes. However, as these ex¬ 
periments were not arranged for the determination of that factor, no 
certain results could be obtained therefrom. During the past season 
the problem again came up, and the writer made a few experiments in 
an attempt to add further data to the question. In this paper are 
given the results of those experiments, together with the results of 
actual commercial fumigation, as carried on in 125 groves in Tulare 
County during July, August and September, 1917, for the control of 
the citricola scale (Coccus citricola ). 
Experimental Fumigation 
The necessary apparatus for the carrying on of these experiments con¬ 
sisted of the following. Two form “trees” of the same size and shape 
were used. These consisted of frameworks of such form that when 
covered with a tent they would approximate the shape of a fair-sized 
orange tree. Each measured 26 feet around by 31 feet over, which 
size requires, according to the schedules in use at present, a six ounce 
charge of sodium cyanide for the 100 per cent or full schedule. They 
were each covered with tents of the same size and material; namely,, 
