24 
BULLETIN 885, U. S. DEPARTMENT OF AGRICULTURE. 
It is seen, therefore, that Ashby (3) is right fundamentally re- 
garding the life history of the black fly. But he did not go far 
enough in his studies. The life history is not clear-cut, as one is 
led to believe from his brief work, and is greatly influenced by con- 
ditions. The total length of time from the egg to the adult as given 
by him and Cardin (11) may be much longer than they indicate. 
Some of the individuals do go through their development in as few 
as 55 days, but there is a great variation and the majority take a 
Fig. 5.— Diagrammatic chart showing method used in keeping record of individuals of Aleurocanthus 
woglumi in life-history work. 
longer time, especially under unfavorable conditions. There is con- 
siderable variation in the length of time that individuals remain in 
each instar, the greatest variation being in the time that they remain 
in the pupal stage. This is true in a colony all of whose individuals 
hatched from the same egg spiral. There seems to be a constant 
dropping back of some individuals so that the group life history is 
drawn out. 
The time for the complete development from egg to adult, as is 
shown by the tables, ranges from 55 (45 the minimum) to 113 (the 
maximum) days. 
