36 PRACTICAL ZOOLOGY 



potato was introduced it transferred its activities from weeds 

 to cultivated potato plants. Since then it has spread all over 



FIG. 18. Insects injurious to field crops : A, cutworm ; B, Hessian fly ; 

 C, green bug or aphid (at the left) being parasitized by a minute wasp ; D, cot- 

 ton bollworm or corn-ear worm ; -E, alfalfa weevil ; F, cotton boll weevil. 

 (After various authors.) 



this country and has become a pest that must be fought con- 

 stantly. There are two broods of beetles per year in most parts 



