42 MASS. EXPERIMENT STATION BULLETIN 189. 



Oviposition of second generation moths occurred within a few days 

 after emergence, and extended over a period of about two weeks. Eggs 

 of the first generation were first secured in Ufe-history cages on May 24 

 (see Table XI). 



Larvee of the first generation were first secured in life-history cages on 

 June 2 (see Table II), and were observed for the first time in the field 

 on June 13. 



The first pupa of the first generation was found in the field on July 11', 

 and in life-history cages on July 15. Maximum pupation took place 

 between July 19 and 23 (see Table IV). 



Emergence of first generation moths began about July 23 and reached 

 its maximum between July 27 and August 4. The last emergence of 

 first generation moths was recorded from indoor cages on August 29 (see 

 Table XIV), and from corn in the field on September 6. 



On July 29 the first eggs of the second generation were secured in life- 

 history cages (see Table V). Eggs of this generation were first observed 

 in the field on August 13. 



Larvse of the second generation were first secured in life-history cages 

 on August 2 (see Table VIII), and were observed for the first time in the 

 field on August 13. On this date some of the larvae in the field were in 

 the second and third instars. On September 2 many of the larvae in the 

 field were in the fifth and sixth instars. When the last field observations 

 were made, on November 30, most of the larvae were in the fifth and 

 sixth instars, and in this stage of their development they probably will 

 pass the winter of 1918-19. 



Seasonal Abundance. 



The larvae of the borer reach their greatest abundance and do the most 

 damage to corn and other host plants during the late summer and faU. 

 The damage to early corn by larvae of the first generation during June 

 and July is much less than the damage to late corn by those of the second 

 generation during August and September. The same is true for the other 

 host plants infested by the insect. 



There is quite a heavy mortality of overwintering larvae, due to natural 

 causes, and this when added to the high percentage of overwintering 

 larvae destroyed by control measures and cultural practices, greatly re- 

 duces the numbers of the pest that remain to perpetuate the species in 

 the spring. Consequently the first generation of larvae is much smaller 

 in numbers each year than the second generation of the preceding year. 



HABITS OF LARViE. 

 Hatching. 



About a day before hatching takes place, the black eye spots and red- 

 dish mandible tips of the developing larva may be seen through the semi- 

 transparent chorion of the egg. A few hours before hatching, the head 



