AUTHOR'S PREFACE 
HE radical changes in conditions during the 
past eight or ten years along agricultural and 
Wi commercial lines have been followed by the 
4 general distribution of many insect pests of a 
serious character. In commercial transactions the dan- 
gers have been so great along certain lines that many 
State laws have been enacted to prohibit the distribu- 
tion of such insects as the San José scale and others of 
a dangerous nature. Some foreign governments have 
enacted such legislation as to make it practically im- 
possible to ship fruit and nursery stock without the 
most rigid inspection and fumigation before entry is 
permitted. 
Ability to successfully combat noxious inse¢ts is a 
problem of the most vital importance to farmers, fruit 
growers, nurserymen, gardeners, florists, millers, grain 
dealers, transportation companies, merchants, grocers, 
housekeepers and others. This is especially true of 
the fruit, nursery, and grain industries. The use of 
hydrocyanic acid gas and carbon bisulphid, two very 
powerful insecticides, have largely solved these serious 
problems. We owe the discovery of carbon bisulphid 
as an insecticide to M. Doyere, while that of hydrocyanic 
acid gas belongsto D. W. Coquillett. Their practical 
application has been one of gradual development. 
With the advent of the San José scale in Eastern 
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