76 
The Bulletin 
of its tunnel where it is feeding. In the insectary the larvae in the 
first day or two after hatching are capable of constructing an enormous 
length of tunnel, comparatively speaking. It is nothing unusual for 
one of these small larvae less than two milimeters in length to burrow 
four or five times the length of a section of cornstalk seventy-five mili¬ 
meters in length in a single day, or more than one hundred and fifty 
times its own length. 
The turning and twisting habits of the prepupal stage of the larvae 
is given in the discussion of the formation of the pupal cells. The 
larva? as they prepare to molt have the same habit of turning about in 
their burrows. This most certainly helps them very much in getting 
rid of the old cast skin, as the larvae usually work themselves forward 
at the same time they are turning; thus they travel in a spiral, and 
the cast skins are gradually worked backward and left eventually in 
the tunnel behind. 
MORTALITY DURING LARVAL STAGE 
In our breeding cages we have tried, in as far as possible, to give 
the larvae natural conditions and at the same time make it possible 
to observe the larvae from day to day. This undoubtedly subjected the 
larvae to conditions which must have been in part, at least, adverse 
to their best development. On the other hand, larvae which were 
observed every day completed their development in the same average 
time as larvae which were disturbed only as often as was necessary to 
provide them with fresh food. 
During the summer of 1915, 265 larvae were isolated and studied 
for mortality data. These larvae were treated in the ordinary way for 
rearing larvae save that they were disturbed only when it was neces¬ 
sary to give them fresh food. The most unnatural condition in¬ 
troduced, so it seemed to the writer, was the fact that the pieces of 
cornstalks sometimes became slightly soured before they were replaced. 
In a few cases it seemed that natural decay, which sometimes sets in 
overnight in our climate, was the cause of the death of the larvae, but 
other larvae were able to withstand a condition which seemed actually 
identical in every respect. So it seems we are safe in concluding that 
the conditions were perhaps comparable with conditions in the field, 
and for the present, at least, we might say that no more larvae die in 
the laboratory under the above conditions than would die in the field 
under natural conditions. 
Therefore the following figures are presented for what they are worth. 
Of the 265 larvae tested for this point, 138 passed through their various 
molts and were able to pupate; in other words, a mortality of slightly 
more than 45 per cent from egg to pupa. 
In our regular breeding cages, where an atempt was made to secure 
every molt, 119 larvae out of 276 died before they were able to pupate. 
