408 



ANIMAL BIOLOGY 



3. Insects Injurious to Plants 



It has been stated, and truly, that it costs the American farmer 

 more to feed his Insect foes than to educate his children: in fact, 

 more than is expended for all the educational institutions in the 

 United States, nearly twice as much as for our military and naval 

 forces, and more than twice the loss by fire. And we all pay the 

 bill. Every kind of plant supports many species of insects, although 

 usually certain ones are especially destructive. Thus Oak trees are 

 attacked by no less than a thousand kinds of insect pests; Apple 

 trees by about four hundred, and Clover and Corn by some two 

 hundred insect enemies. A few random examples obviously must 

 suffice for our view of the field. 



The Army-worm is the larva of a brown Moth which sometimes 

 becomes so numerous in regions east of the Rocky Mountains 

 that the caterpillars have to migrate in search of food. Immense 

 armies crawl along totally destroying the crops over large areas. 

 Fortunately, the pest has its own insect enemies, the chief being 

 certain Tachina Flies which lay their eggs on the caterpillars, and 

 the larvae of the flies burrow into their bodies and finally destroy 

 them. (Fig. 266.) 



Of equal interest is the Carrage Butterfly which was ac- 

 cidentally introduced from Europe into Canada in 1868, and has 



ih> — «& 



Larva 



'"''"".I, .,•'''' 



'in ■ •.-■.-*: 

 ""hihiim"**' 



Chrysalis 



Adult 



Fig. 259. — Life history of the Cabbage Butterfly, Pieris rapae. 



gradually made the whole of the United States its field, even oust- 

 ing a related native species. Many of the caterpillars of the Cab- 

 bage Butterfly are destroyed by parasites; one being a Brachonid 

 Fly which was imported from its old home in Europe by entomol- 

 ogists for this special purpose. (Fig. 259.) 



