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Duration of the Larval Stage on Various Hosts 
Duration of the larval stage on alfalfa, hubam, and sourclover was 
determined by bulk cage rearings begun on January 29 and 30 under insectary 
conditions where temperatures were 2 to 4 degrees higher than those in the 
field. Each rearing consisted of a single cage for each host supplied with 
30 to 50 newly hatched larvae. Six such rearings were made during the sea- 
son. Cages used were ordinary jelly glasses with a moistened disk of blot- 
ting paper in the bottom and a perforated tin lid which prevented too rapid 
evaporation and drying out of food. Usually examinations were made daily 
and fresh food was supplied. 
Initial results indicated that larvae reach maturity in approximately 
1 month, developing slightly faster on alfalfa than on other hosts. This 
period decreased considerably for each successive rearing as the season ad- 
vanced, being only about 3 weeks by the end of the season. In every 
rearing larvae required slightly less time to mature on alfalfa than on 
sourclover or hubam, which appeared about equal. 
Data showing the comparative development, by stages, of larvae on 
different hosts are given in table 4. 
Larval Abundance and Development in the Field 
The first newly hatched larvae appeared in alfalfa early in January 
but very few were present as late as January 15, although the abundance of 
eggs gave promise of a sizeable population. In spite of early expectations 
and continued oviposition, larvae never attained an abundance commensurate 
with that of eggs. Of the relatively small larval population which appeared, 
only a small fraction developed to the second stage and still fewer to suc- 
ceeding stages. Apparently some factor or factors prevented normal survival 
and development on alfalfa during the 1940 season. Occasional dead larvae 
were observed following a period of frosty nights during the latter half of 
January, and their death was attributed to that factor, since with the ad- 
vent of favorable weather larvae quickly doubled in abundance. The popu- 
lation again declined following a second cold period beginning early in 
February and continued to do so during the remainder of the month. This was 
due in part to a decline in oviposition, but the principal factor was mor- 
tality. The fact that high larval mortality in alfalfa persisted even after 
the advent of warm spring weather strongly indicated the unsuitability of 
alfalfa as a larval host. 
Information on the abundance "and development of larvae on sourclover 
v/as not obtained during January, since this plant did not show appreciable 
growth until late in the month. Early in February, however, observations 
revealed larvae to be more numerous in sourclover than in alfalfa fields, 
and this was even more apparent late in the month. Frosty nights apparently 
affected the population in the same manner as in alfalfa, but the decrease 
