30 



MASS. EXPERIMENT STATION BULLETIN 189. 



LIFE HISTORY. 



FiEST 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 7.43 days. 



Maximum length of incubation period 9 days. 



Minimum length of incubation period, 5 days. 



Larval Period. 



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

 various parts of their food plant, and pass through 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 



