- 16 - 
The newly formed pupa is usually light green but as development progresses 
it gradually assumes the structure and light-bronze color of the adult. The 
exoskeleton of the newly- formed adult is thin and soft, but in a few days it 
hardens and the adult is able to emerge from the cocoon. 
Duration of the Pupal Stage 
The duration of the prepupal and pupal periods was determined by con- 
tinuing larval rearing cages until the emergence of adults. 
During the early part of March the length of the prepupal period ranged 
from 4 to 11 days and averaged 4.0, 4.3, and 4.9 days, respectively, for 
larvae reared on sourclover, hubam, and alfalfa. The duration of the pupal 
stage on these hosts ranged from 12 to 21 days and averaged 9.0, 11.1, and 
10.2 d^ys, respectively. The length of the enxire pupal period on sourclover, 
hubam, and alfalfa, respectively, was 13.0, 15.3. and 15.1 cays. Both the pre- 
pupal and pupal stages required fewer days during the remainder of March, 
and there vras no significant difference attributable to the larval food. 
The final rearing begun early in April revealed a marked shortening of the 
prepupal and pupal stages, with the entire pupal period requiring only 6.2 
to 6.8 days. Adults remained in cocoons 2 to 5 days before emerging but 
most of them emerged in 2 to 3 days. 
Data on the approximate duration of the pupal period are shown in 
table 6. 
Abundance and Development in the Field 
Ecological studies in an infested alfalfa field throughout the 1940 
season failed to reveal a cocoon containing either a larva or pupa, and 
only one empty cocoon was encountered. Many other fields were examined,, but 
in only a few was an occasional cocoon observed. This clearly indicated 
that very few larvae survived and developed to maturity in alfalfa. 
Similar studies in a heavily infested sourclover area showed that 
only a small proportion of a sizeable larval population survived to spin 
cocoons. Furthermore, only a minor portion of cocooned individuals reached 
the adult stage. This condition also prevailed in the many other sourclover 
areas observed. A portion of the mortality within cocoons probably was 
attributable to the same factor or factors that affected the larval popu- 
lation. There were, however, several known factors involved, principally 
exposure to the sun, and parasites. The combined effect of the various 
factors influencing abundance and survival of pupae is shown by the dat? 
given in table 7. 
