The Tea insects of India. 



Hydrocyanic Gas. 



The Hydrocyanie eras treatment consists in throwing a moveahle 

 tent over the bush so as to confine the air and then fumig-ating the ia- 

 terior with Hydrocyanic gas. The gas is produced in the simplest pos- 

 sible manner by slipping inside the tent a saucer containing a little 

 weak sulphuric acid into which a lump of potassium cyanide is dropped. 

 The system hns only been invented during the past few years, but is said 

 to have already been adopted upon a very large scale for the destruction 

 of scale insects upon orange trees in California. When carefully applied 

 it is claimed to destroy, not only scale insects, but also almost every other 

 form of animal life inside the tent, without injury to the orange tree, 

 and it is likely to be almost equally satisfactory for tea bushes. In this 

 case only a very small tent would be required and the whole process 

 could easily be worked by a couple of coolies trained for the purpose. So 

 promising indeed does it appear for use upon tea gardens that it is only 

 surprising it has hitherto attracted so little attention. 



The following extract from a report by Mr. D. W. Coquillet, pub- 

 lished in the United States Department of Agriculture, Division Ento- 

 mology, Bulletin No. 23, gives all the necessary particulars concerning 

 the treatment, so far as orange trees are concerned. For tea bushes the 

 only modification likely to be required is to reduce the size of the tent 

 and to use proportionately less of the chemicals. 



" Briefly speating, this process consists in covering the infested tree with an air- 

 tight tent, and afterwards charging the tent with hydrocyanic gas. The material com- 

 monly nse'd in the construction of the tent is what is known as blue or brown drilling. 

 A few persons have used ducldng instead of the drilling, but this is much inferior to 

 the latter ; in the ducking the threads of which it is composed extend only lengthwise 

 and crosswise, whereas in the drilling they also extend diagonally— this belonging to 

 the class of goods to which our merchants apply the term " twilled " — and for this 

 reason the drilling is both stronger and closer in texture than the ducking. 



" After the tent is sewed up it is given a coat of black paint, as it has been ascer- 

 tained that tents treated in this manner last longer than those which have been simply 

 oiled with linseed oil. Some persons mix a small quantity of soap suds with the paint 

 in order to render the latter more pliable when dry, and therefore less liable to crack ; 

 instead of thus painting the tent some persons simply give it a coating made of an 

 inferior glue called " size," first dissolving this in water and then covering the tent 

 with it, using a whitewash brush for this purpose. Sometimes a small quantity of 

 whiting or chalk (carbonate of lime, Ca C03) is added to this sizing with or without 

 the addition of lamp-black. A few make use of the mucilaginous juice of the common 

 actus {Opuntia engelmanni, Salm.) for this purpose ; to obtain this the cactus 

 leaves or stems are cut or broken up into pieces, thrown into a barrel and covered with 

 water, after which they are allowed to soak for three or four days ; the liquid portion 

 is then drawn off, and is ready for use without further preparation. Tents which I 

 saw that had been prepared with this substance were to all appearances as air-tight 

 and pliable as when prepared in any other manner. 



