44 ECONOMIC ENTOMOLOGY 



effectiveness of the primary. Frequently, however, these secondary 

 forms are infested with tertiary parasites. 



In the control of injurious forms it is evident that primary parasites 

 are beneficial, secondary harmful and tertiary beneficial, on the other 

 hand, when beneficial insects are parasitized the primary are harmful, 

 the secondary beneficial and the tertiary harmful. 



Insects and Birds 



When it is known that about two-thirds of the food of our common 

 birds consists of insects, it becomes evident that the agency of birds 

 in the control of insects is of the highest importance. The seasonal 

 diet of the robin, bluebird, catbird, king-bird, flycatchers, chickadee, 

 wren, swallow, woodpecker, cuckoo, night-hawk, warblers, oriole and 

 many other birds has been carefully studied in recent years, with the 

 resulting discovery that insects form in most cases their only food, and 

 only at certain seasons are small fruits eaten. 



Birds are no doubt of special value to the farmer in nipping incipi- 

 ent scourges in the bud on account of their ability to move rapidly from 

 place to place in search of food, and on account of their varied character 

 and habits. Especially is this true of our winter birds which search 

 every cranny and nook for the hibernating forms of insects at a season 

 when every form destroyed means in most cases the absence of hundreds 

 or thousands of their progeny the following summer. 



An international treaty between Great Britain and the United 

 States for the protection of migratory birds in the United States and 

 Canada was signed in Washington in August, 191 6. For many years the 

 numbers of such birds had been decreasing to such an extent, through 

 careless and indiscriminate slaughter, that the agricultural and forest 

 crops of the two countries were in danger of suffering serious losses 

 from insect depredations. It was deemed advisable, therefore, in 

 the interests of the two countries to adopt a uniform system of bird 

 protection, such as the treaty provides. The most important provision 

 relates to close seasons, viz: (i) a close season on migratory game 

 birds from March loth to September ist except for maritime shore 

 birds when the close season is from February ist to August 15th; 



(2) an open season for three and one-half months for wild fowl; and 



(3) a close season throughout the year on insectivorous birds. 



