10 BULLETIN 535, V. S. DEPABTMENT OF AGEICULTUEE. 



very numerous, the petiole is tunneled to the extent that it shrinks 

 considerably and causes the leaf to wither and die at the tip and 

 about the margins. When the larva is ready for pupation, it leaves 

 the petiole and enters the ground. The exit holes, which soon collapse 

 and appear as brown spots, are also characteristic of larval injury. 



When both larvae and adults occur together, the former are the 

 more injurious. The injury which the adults cause to the young 

 shoots early in spring as they are breaking through the soil is pos- 

 sibly more serious than subsequent injuries. 



That the larva may live in the roots of the plant has been' clearly 

 demonstrated since it was first reported to the senior author. A 

 potted plant died and was left intact for about a month. When the 

 pot was wanted for another experiment the soil was found to con- 

 tain several larvae and pupae. Only the shell of a root remained, the 

 contents having been completely devoured by the larvae. The pupae 

 transformed to normal adults shortly afterward. This habit of de- 

 scending to the roots is not very general, however, for it has never 

 been observed while roots peeled for the shredder were being ex- 

 amined. 



After leaving the plant the larva enters the soil to a depth of from 

 one-eighth to one- fourth of an inch or even 3 inches. Here it re- 

 mains for 4 or 5 days, when it becomes white and short and thick. 

 In this form it is inactive. From 2 to 6 days, usually 3 or 4, inter- 

 vene before pupation. 



The total larval period of an individual which was deposited as 

 an egg on May 1, and which was hatched about May 15, was 48 days 

 (about May 15 to about July 6). Another required 52 days; two 

 others required about 57 days, two others 64 days, and two others 

 66 days. 



The two larvae which developed in 48 and 52 days, respectively, 

 each remained 10 days in the pupal stage. Three other individuals 

 also passed the pupal stage in 10 days, but .one required 12 days, 

 while three required from 12 to 13 days. 



On September 11, 1915, a few pupae in the cages had not yet trans- 

 formed. April 17, 1915, the adults were already numerous about the 

 ground where the shoots of horse-radish were just appearing, or 

 about to appear. 



This flea-beetle, like others of its kind, and like most leaf-beetles, 

 hibernates in the adult stage. Careful search for pupae from time to 

 time practically proves this. 



In Wisconsin only one generation appears annually. 



The total period of time from egg laying to adult ranges from 77 

 days to about 90 days in the cases where complete records were 

 obtained. Repeated attempts to obtain eggs from the adults of the 

 current season failed. 



