S. D. A., B. E. Bui. 90, Part I. Issued May 13, 1911. 
HYDROCYANIC-ACID GAS FUMIGATION IN CALIFORNIA, 
FUMIGATION OF CITRUS TREES. 
By R. S. Woglum, 
Special Field Agent, Bureau of Entomology. 
HISTORICAL. 1 
To Mr. D. W. Coquillett, of the Bureau of Entomology, United 
States Department of Agriculture, belongs the credit of first deter- 
mining the great value of hydrocyanic-acid gas for destroying insect 
pests on plants. During the fall of 1886, while a special agent of 
what was then the Division of Entomology, experimenting upon the 
cottony-cushion scale {leery a purchasi Mask.) in orange orchards in 
California, he discovered this gas to be a most efficient insecticide for 
scale-insect pests of citrus trees, and his continued experimental 
work placed its use on such a practical basis that by 1890 it had com- 
menced to be employed quite extensively in a commercial way. 
The use of this gas was restricted to California until the winter of 
1892-3, during which time Prof. H. A. Morgan gave it a trial on 
orange trees in southern Louisiana. The following year, 1893, found 
it on trial against the San Jose scale in Virginia and against citrus 
insect pests in Florida, in Montserrat, British West Indies, and in 
Cape Colony, South Africa. Its subsequent development and use 
has been rapid as well as extensive, so that to-day fumigation of citrus 
trees is carried on in California, Florida, Australia, Japan, and the 
colonies of South Africa. At the time of this writing the practice is 
being introduced into Spain and Porto Rico. 
The great success attending the hydrocyanic-acid-gas treatment 
against the scale pests of citrus trees soon brought about its intro- 
duction into a broader field of activity. This gas was given its first 
trial on deciduous trees by Mr. D. W. Coquillett in 1894 at Char- 
1 The Canadian Entomologist for 1877, volume 9, pages 139-140, contains mention of an experiment by 
James T. Bell in which an insect cabinet was freed from insect pests by dropping sulphuric acid on 
potassium cyanid. This is the first record, so far found, of the rapid development of the gas by combin- 
ing sulphuric acid with lump cyanid with the object of killing insects. The use of cyanid, however, as a 
means of killing insects in collectors' bottles is very old. The gas liberated from moistened lump cyanid is 
the same as that generated by the action of sulphuric acid or hydrochloric acid, on the authority of Dr. 
J. K. Haywood, of the Bureau of Chemistry of this department. The action of the acid merely hastens 
the generation of the gas. It does not seem desirable or appropriate, therefore, in a discussion of the 
broad-scale economic use of this gas for the destruction of insects in orchards or in buildings, to consider 
these much earlier and minor uses of the gas by collectors for killing insects, or similar limited uses. — 
C. L. M. 
1 
