allliougli a considorable lunnber, parasitic or i)r0(hu'0()us on otlior in- 

 sects, arc iiulirectly beneficial to it by relieving it to some extent from 

 the attacks of insect enemies. Several of them tlo no appreciable harm 

 at any time; others are injurious only under special conditions more or 

 less rare; and still others are injurious to it whenever and wherever they 

 occur. Their coiumon interest in this one plant of course brings these 

 insects also into important relations to each other, like those which 

 influence any local assemblage of animals — those of a pond, of a grove, 

 or of a barnyard, for example — and make of them a related group in- 

 stead of a mutually indifferent assemblage. 



It is the object of the present report to discuss this entire group of 

 corn insects, to the end that the teacher and student, of whatever grade, 

 may find in this paper a clue to the whole system of insect life of which 

 the corn plant is the center. The study here presented may thus stand 

 as in many respects a type or example of the relations of a plant to its 

 insect visitants. While in this treatment the economic features of the 

 system will receive full attention, this will not be to the exclusion of 

 featm-es of scientific or educational interest merely; but to avoid encum- 

 bering the more important economic matter with details and discussions 

 of secondar}^ interest, the i)aiier is divided into sections, based on the 

 economic relation. 



Dnisioxs OF THK Corn Ixskct (iHonp. 



The entire assemblage of corn insects is nuich too large and compli- 

 cated for convenient discussion as a whole, and it may conseciuently 

 best be divided into subordinate groups, some corresponiling to the 

 different organs and structures of the corn plant itself, others to difTerent 

 stages of its growth, and si ill others to the previous history of the land 

 on which the corn is grown or to the situation of the field with resjiect 

 to other and adjacent crops. There is, for example, a small group of 

 insects which become abundant in corn fields only where corn is grown 

 on the same gromul year after year — the corn root-worm is an instance — 

 while others, like tlie wireworms, infest corn injuriously only when this 

 follows within a year or two upon grass, and others, like the stalk-borer, 

 may invade corn only from grass-lands outside. The corn root-aphis 

 makes its main attack on the crop while the plant is yomig. and the 

 leaf-aphis usually does not appear until the crop is well advanced, and 

 continues in rapidly increasing munbers until frosty weather checks its 

 multiplication. 



Among the groups corresponding to the difTerent parts and organs of 

 the growing plant the most definite distinction is between those especially 

 adapted to a life under ground, and those which never enter the earth 

 in search of fooil. The white-grubs, wireworms. corn root-worms, seed- 

 <'orn maggot.s, and root-lice are on one side of this dividing line, and the 



