30 



MASS. EXPERIMENT STATION BULLETIN 189. 



LIFE HISTORY. 

 First Generation. , 



Incubation Period. 

 The eggs are deposited in masses of from 5 to 50 on the under surface 

 of the upper blades of corn or other food plants. They hatch, on an 

 average, in 7 days, with a maximum of 9 days and a minimum of 5 days 

 (see Table II), the duration of the incubation period depending somewhat 

 upon temperature conditions. 



Average length of incubation period. 

 Maximum length of incubation period, 

 Minimum length of incubation period, 



7.43 days. 

 9 days. 

 5 days. 



Larval Period. 



In the course of their development the larva? feed upon, and within, 

 various parts of their food plant, and pass tlirough from five to eight 

 instars. Out of a total of 20 individuals reared from egg to pupa, in 

 life-history cages 14 individuals required five instars to complete their 

 larval growth, 3 required six instars, 2 required seven instars and 1 indi- 

 vidual eight instars. It is probable that, under field conditions, there are 

 normally five or six instars in this generation. 



In 20 life-history cages the average duration of the first instar was 



