]^0. 5.] Gas Treatment for Sc'ih Insech. 13S 



GAS TREATMENT FOR SCALE INSECTS. 



{An extract from Uie Report of Mr. D. If. Coqnillet, puhlia/ied in the U' 

 S. Department of Agncidtnre JJivisioti Entomology , Bulletin No. 23.) 



[The following report on g-as treatment for the scale insect Aspidiotus 

 uurantii, Maskell, is of interest as both coffee and tea in India suffer 

 largely from scale insects, which could no doubt be destroyed by any 

 treatment that is found to answer with the orange scale. The chief diffi- 

 culty in aj)pl}'ing the gas treatment to orange scale seems to be owing to 

 the size of the orange trees, as this necessitates the employment of tents 

 of considerable dimensions. Tea and coffee shrubs, therefore, being very 

 much smaller than orange trees, would seem to be more favourably con- 

 stituted for the treatment. According to Mr. A. E, Shipley (Kew 

 Bulletin No. 57, 1891) the gas treatment has been used on a very ex- 

 tensive scale in California, some 20,000 trees in orange country alone 

 being treated by it in 1S90, and Mr, Coquillett states that he has not 

 heard of any accident resulting from the gas, though great care is neces- 

 sary in using it owing to the fact that it is j^oisonoiis to ma.n and other 

 animals. — Ed.] 



" Brieflj speaking, this process consists in covering the infested tree with an air- 

 tight tent, and afterward cliarging the tent with hjdroc3'anic gas. The material com- 

 monly used in the construction of the tent is wliat is known as blueor brown drilling, 

 A few persons have used ducking 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 diajronally — this belonging to 

 the class of goods to which our merchants applj' 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 coiit of black paint, as it has been ascer- 

 tained that tents treated in tliis manner la.st 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 tlius 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 Cog), is added to this sizing with or without 

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

 Cactus (Opvntia 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 thiee or four days; the liquid portion 

 is then drawn off, and is ready for use without farther 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 mannev. 



"A tent 26 feet tall by 60 feet in circumference — a size large enough to cover the 

 largest orange tree now growing in this State — if made out of drilling, and either 



