170 
Psyche 
[December 
continuous food supply to make a two-year developmental 
period possible. If the larval stage does actually last more 
than twelve months it should be possible to find larvae at any 
time during the year. Although it may be a possibility to 
find these larvae at any time the probability is very small, at 
least in the vicinity of Urbana, Illinois, which is very near 
the eastern limit of the range of this insect. Only 38 adults 
of T. femoratus were seen during the summer. A conserva- 
tive estimate of the number of adults of T. tetrophthalmus 
seen during this period would be 8,000. An average of one 
plant out of three was found to be infested by this latter spe- 
cies. It can, therefore, be shown mathematically that there 
would be one chance in approximately 630 of finding a plant 
infested with T. femoratus. This again would be a conserv- 
ative figure. The duration of the larval stage of any one 
individual is not known, however, it seems probable that it 
would be at least 23 months. 
