20 



mains when all else has been tried. In case of fruit and other 

 trees starvation is impracticable ; but when field crops are attack- 

 ed, as a last resort this may be tried. That is, the infested field 

 may be allowed to lie fallow for a year or two, in order that there 

 may be no food for the insects. Sometimes a simple change of 

 crop answers the object. To be successful, all farmers in a given 

 locality should act in concert, else starving out on one farm would 

 be of no avail, if the pest were allowed to increase or even exist 

 on those joining, from which the farm freed by starvation would 

 be speedily stocked. 



HYDROCYANIC ACID GAS. 



Another insecticide has been used with some degree of success 

 in California, where scale insects have been at times very trouble- 

 some. By this method only small trees, or those of no great size, 

 can be treated. It consists in covering each tree with a tent made 

 for the purpose and fumigating it with Hydrocyanic acid gas. As 

 described by D. W. Coquillett in Insect Life as follows : " It 

 consists in using one part by weight of dry or undissolved potas- 

 sium cyanide, with one part of sulphuric acid and two parts of 

 water. The generator is made of lead and is somewhat of the 

 form of a common water pail. After the tent is placed over the 

 tree, the necessary quantity of dry cyanide is placed in the genera- 

 tor, the proper quantity of cold water is added, and the generator 

 placed under the tent near the trunk of the tree ; the acid is then 

 added to the materials in the generator, a sac thrown over the top 

 of the latter, after which the operator withdraws and a quantity of 

 earth is thrown upon the lower edge of the tent where it rests 

 upon the ground to prevent the escape of the gas. After the ex- 

 piration of fifteen minutes the tent is removed and placed over an- 

 other tree." This treatment does not, if care be taken as to quan- 

 tity of material, etc., injure the foliage or fruit, but does wholly des- 

 troy the insects and at no great cost. I have quoted thus fully 

 from Mr. Coquillett's article because the same process is applicable 

 to other trees in other places, and would prove effectual when 

 everything else fails. It should be always used with care and by 

 one who understands fully what he is dealing with, as the gas is 

 exceedingly poisonous, and must not on any account be breathed. 



BORDEAUX MIXTURE. 



What is known as the Bordeaux Mixture, though not an insecti- 

 side, may properly be mentioned here for in combination with poi- 



