18 MASS. EXPERIMENT STATION BULLETIN 189. 



Medford, Mass., were carefully dissected and counts made of the larvae 

 found therein, in order to secure data concerning the number infesting 

 single plants. A maximum of 117 larvse, and a minimum of 7, with an 

 average of 46 laryse per plant, were found in these 75 plants. These 

 plants composed a total of 17 hills taken at random in different parts of 

 the field. A maximum number of 311 larvae, and a minimum of 151, 

 with an average of 206 larvse per hill, were found in these 17 hills of corn. 

 The 17 hills of corn composed of 75 plants contained a total of 3,503 larvae. 

 The actual count of one-eighth of an acre in tliis field showed a total of 

 2,855 plants, or 22,840 plants to the acre. Each of these 2,855 plants 

 was infested to a greater or lesser degree. An average infestation of 

 46 larvae per plant, as shown above, means a total of 1,050,640 larvae of 

 the European corn borer per acre of corn. 



Natm-ally, this extensive injury to the interior of the cornstalk, to- 

 gether with the numerous entrance and exit holes of the larvse on the 

 surface, weakens the plant to such an extent that it soon breaks over and 

 lies prone upon the ground. The supply of nutriment to the ear is also 

 cut off, causing a small or aborted ear of corn. Even when only a few 

 larvae are 'present within the plant, the growth of the stalk and formation 

 of the ear are greatly retarded. 



The tunnels left by the larvae of the European corn borer frequently 

 serve as sources of infection by various rots and fungi, so that the interior 

 of badly infested stalks is sometimes found to be a mass of putrifying 

 matter, occupied by various scavenger insects that have gained ad- 

 mittance to the plant by way of the entrance or exit holes of P. nvbilalis 

 larvae. 



Injury to the Ear. 



The indirect injury to the ear by larvae of the European corn borer has 

 already been mentioned. This is caused (1) by interference with proper 

 poUenization resulting from larvae cutting off the tassel, and (2) by inter- 

 nal injury to the stalk, which cuts oft" the normal supply of nutriment 

 to the ear. 



The ear, however, is also directly injured by the ex-ternal and internal 

 feeding of the larvse. Frequently the moths of the first generation, and 

 habitually those of the second generation, deposit their eggs directly 

 upon the silk of the ear. The newly hatched larvae feed first upon the 

 silk, thus contributing to improper fertihzation, and later they work 

 their way down into the ear, where they tunnel through all parts of the 

 cob and also feed upon the newly formed kernels. Sometimes eggs are 

 deposited upon the exterior, or husk, of the ear, and the newl}^ hatched 

 larva feeds for a time upon the exterior of the husk before entering the 

 ear, either at its tip end, or between the edges of the leaves of the husk. 



The ear is frequently entered by partly grown larvse, which have left 

 some other plant or another part of the same plant. These larvse may 

 enter the ear at any point, — its tip end, along the sides, or through the 

 side of the pedicel. In other instances they tunnel directly from the in- 



