14 



BULLETIN 1238, U. S. DEPARTMENT OF AGRICULTURE 



Table 4. — Length of larval feeding period of fall cankerworm, Wallingford, 

 Conn., 1919 and 1920. Summary' of Table 8. 



Number of days. 



Number of larvae. 



In 1919. 



In 1920. 



28 , 



1 







16 



33 



65 



31 



10 



5 







3 



1 























17 



34 



18 



15 



10 



5 



1 



1 



3 



1 







1 



29 



30 



31 



32 



33 



34 



35 



36 



37 



38 



39 



40 



41 



Total 



165 



106 



Average length of feeding period in days... . 



32.1 



32.2 



Table 5 records observations on the average length of the differ- 

 ent larval stages of the fall cankerworm at Wallingford during 1919 

 and 1920. 



Table 5. — Average length of larval stages of fall cankerworm, 



Conn., 1919 and 1920. 



Wallingford, 



' 



1919 



1920 



Stage. 



Number 

 of larvae. 



Number 

 of days. 



Number 

 of larvae. 



Number 

 of days. 



First 



255 

 213 

 195 

 165 



13.27 

 5.85 

 5.13 

 7.94 



127 

 115 

 112 

 106 



11.18 





5.38 



Third 



5.21 





10.51 







Total 





32.2 





32.3 











It will be noted that the total larval feeding period in Table 5 

 differs slightly from that given in Table 4, which is based only on 

 those larvse completing their development, while the data in Table 

 5 are based on different numbers of larvae in the successive stages. 



ENTERING THE GROUND. 



For cocooning and pupation the larvae enter the ground to a depth 

 of several inches. In battery jars containing about 6 inches of loose 

 soil, they go down about 2J inches. In the field the depth varies 

 according to soil conditions. 



To all external appearances the cocoon is complete about 24 hours 

 after the larva has entered the soil, although in some cases its con- 

 struction may take 48 hours. 



Table 6 shows the dates the larvae entered the soil in 1919 and 1920. 

 On June 25, 1920, two days after the last larva under observation in 

 the insectary at Wallingford had entered the ground, several larvae 

 were noted at Milford, Conn., about 24 miles southwest of Walling- 



