THE EOITGH-HEADED CORN STALK-BEETLE 13 



5 to 8 weeks after hatching — usually this is about a week or 10 days 

 before it is ready to enter the prepupa stage. 



DURATION OF THE LARVAL PERIOD 



The length of the larval period in the experimental series varied 

 from 44 to 94 days. In the majority of cases, however, it falls be- 

 tween 50 and 65 days, a fair average being about 57 days. Instances 

 in which the duration of this stage was greater than this mostly 

 belong to those larva? which developed late in the season, when low 

 temperatures retarded their growth. 



The earliest date at which larva? have been found at Tappahan- 

 nock is June 19. This was in 1916, when a few were hatched from 

 eggs collected in the field on June 5. In the breeding experiments 

 of 1915, larva? were still being hatched as late as November, but 

 this was evidently abnormal, as there is no evidence that any are 

 ever hatched in the field later than the first part of August. The 

 latest date on which the young larva? have been found in the field 

 is August 12. This was in 1916, when two were obtained in the old 

 pasture at Tappahannock. The latest date on which full-grown 

 larva? have been observed in the field is November 2. This also was 

 in 1916, when W. T. Emery recorded finding a few larva? of what 

 he supposed to be this species in the same pasture. These specimens 

 were unfortunately lost before their specific identity could be fully 

 established. As the early fall of 1916 was unseasonably cold, it is 

 not unlikely that such an extension of the larval period as is in- 

 dicated by Mr. Emery's observation may have occurred. 



Although it is possible that the latest developing larva? may, in 

 some instances, fail to reach maturity before winter, there is no 

 evidence that any ever survive until the following spring. Both 

 field observations and experiments to test this possibility have given 

 only negative evidence. At Charlottesville the larva?, each in its 

 own box, were buried in a compost heap on the approach of winter, 

 but when the boxes were dug out and examined in the spring all 

 the larva? were dead. 



MOLTING 



Experiments to determine the number of molts and the duration 

 of the periods between molts were made at Charlottesville. Each 

 larva upon hatching was transferred to a salve box, the bottom of. 

 which was covered with a disk of moist blotting paper on which 

 were placed a few particles of old cow manure, which had been 

 previously fumigated with chloroform. These experiments were 

 begun August 14, 1915, and were continued throughout the fall and 

 early winter. After September 25 the larva? were kept indoors, 

 where they were subjected to artificial heat. • The mortality in these 

 experiments was high, even after vegetable mold had been' sub- 

 stituted for the manure. Consequently only a very small propor- 

 tion of the larva? completed their development. 



Owing to the late date at which these experiments were begun 

 the time intervals recorded between successive (molts can have little 

 significance as regards the duration of these intervals under field 

 conditions. 



