GAS TREATMENT FOR SCALE 

 INSECTS. 



INTRODUCTORY. 



To the researches of American investigators and the experiences 

 of her fruit growers is due the credit for great improvements in 

 insecticidal washes now used in many different parts of the world ; 

 and to the same source we owe the introduction of hydrocyanic acid 

 gas for the destruction of scale insects in the orchard. The exped- 

 iency of a gas as an insecticide for scale nsects on citrus and other 

 evergreen trees arises from the practical impossibility of reaching 

 all the insects with a liquid on any but small trees ; invariably, some 

 escape destruction 011 large trees and these become the nuclei of 

 new colonies of the insects, which soon become as great a pest as 

 before. 



The destruction of insects by fumigation with poisonous gases or 

 vapours has long been carried on in greenhouses ; but that the pro- 

 cess could be economically practised in orchards remained to be 

 demonstrated in California little more than a decade ago. In the 

 first report of the Board of State Horticultural Commissioners of 

 California, published in 1882, unsuccessful experiments with steam 

 to destroy scale insects on tent-covered trees without injury to the 

 foliage are recorded by Commissioner S. F. Chapin. A few years 

 later, Alexander Craw, the present entomologist of the California 

 State Board of Horticulture, and Mr. J. W. Wolfskill carried on 

 many experiments with a number of different gases. The work of 

 these gentlemen impressed D. W. Coquillett, then a special agent of 

 the Division of Entomology of the United States Department of 

 Agriculture, and the three united their efforts. Mr. Coquillett soon 

 discovered the value of hydrocyanic acid gas for the purpose. This 

 happened in the latter part of the year 1886. In a short titoe, 

 fruit growers began to avail themselves of the discovery ; at first 

 slowly, and then more rapidly as improved methods of applying the 

 gas were devised until the " fumigation process " superseded to a 

 very great extent the use of washes on citrus trees in California. 



