376 ECONOMIC ENTOMOLOGY 



as the Hessian-fly, the pea-weevil, the codling moth, the San Jose 

 scale, the plum curculio, the apple maggot, grasshoppers and many 

 others (Fig. 244). 



4. Natural Enemies of Insects. — (a) Farmers and fruit-growers 

 can do much to encourage the presence of insectivorous birds among 

 the crops. These birds are most important in keeping injurious 

 insects under control. 



Fig. 244. — The San Jose scale. {After Alwood.) 



(b) Frequently, too, hogs and poultry can be utilized to advantage 

 in destroying white grubs, cutworms, grasshoppers, asparagus beetles, 

 etc., in infested fields. 



(c) Lady-bird beetles, ground beetles, and other predaceous insects 

 should be protected as far as possible (see Section relating to the 

 Utilization of Parasites, p. 401). 



5. Restriction and Exclusion of Foreign Insects. — It has been fre- 

 quently pointed out in the preceding pages that many of the most 



