38 



MASS. EXPERIMENT STATION BULLETIN 189. 



Three of the larvse, confined in the life-history cages mentioned, formed 

 pupse during September and October (see Table IX). This is believed 

 to have been caused by the abnormal conditions which inevitably exist 

 in confinement. No pupse of this generation were found in the field 

 during the dissection of many hundreds of badly infested plants throughout 

 the months of October, November and early December, 1918. 



The second generation larvse of the borer normally pass the winter 

 within their host plants as full-grown, or nearly full-grown, larvae in the 

 fifth and sixth instars. With the advent of warm weather in the spring 

 the larvse begin feeding again, and pupate within a short period of time 

 thereafter. 



Pupal Period. 



Pupation occurs in a similar manner to that described for the first 

 generation. The duration of the pupal period for 35 individuals con- 

 fined in life-history cages averaged 17 days, with a maximum of 20 and a 

 minimum of 14 days (see Table X), depending upon weather conditions. 



Table X. — Duration of Pupal Period, Second Generation. 



