THE CONTROL OF INJURIOUS INSECTS 377 



destructive insects are imported forms. Until recent years no effort 

 had been made to exclude foreign insects, but now a rigid inspection 

 of plants which may harbor dangerous pests occurs at the ports of 

 entry. In some cases plants are subjected to fumigation with hydro- 

 cyanic acid gas. 



That such restriction and exclusion are very important is evident 

 in view of recent experiences with the brown-tail moth, the white 

 Ermine moth, the Mediterranean fruit-fly, and others. On the other 

 hand it is advisable to import foreign species that prey upon other 

 foreign insects already here as was done in the case of the gypsy moth 

 and the cottony cushion scale. 



B. ARTIFICIAL OR REMEDL/VL METHODS 



Artificial methods may be conveniently classified as follows: 



1. The application of poisons against biting insects. 



2. The application of contact substances against sucking insects. 



3. The use of poisonous gases. 



4. The application of repellent substances. 



5. The use of protectors. 



6. The use of traps and trap crops. 



7. The use of ditches. 



8. The use of hopperdozers, etc. 



9. Collecting, digging out, jarring, etc, 



10. High and low temperatures. 



I. The Application of Poisons for Biting Insects 



(Consult Farmers' Bull. 908, U. S. Dep. Ag.) 



The three essentials of a good insecticide are: 



(a) Effectiveness against insects. 



{b) Cheapness, both with regard to material and application. 



(c) Harmlessness with regard to insect hosts. 



With regard to Effectiveness, an insecticide must be applied: 



(a) In the proper manner. 



(b) At the proper time. 



When the application of the insecticide is made in the form of a 

 spraysome form of pump is necessary. In small yards and gardens 



