170 
Journal of Agricultural Research 
Vol. XXXI, No. 2 
ferences in degree. Stated in another way, this means that the larval 
period is one in which accumulation of material of the same kind and 
with the same properties goes on from the first establishing of the 
larva within the bean to its final maturity as a larva, while with the 
pupa histolysis and histogenesis produce changes in the chemical and 
physical constituents of the body contents, these changes varying 
with the age of the pupa. With the advent of the adult these 
changes are completed and the short period of quiescence before 
emergence simply permits of a hardening process taking place 
whereby the chitin becomes hard and brittle. 
EFFECT OF INJURY ON THE INSECT’S RESISTANCE 
Early in the course of the work the question as to the effect of injury 
on the resistance of these insects was recognized. Practically all the 
work of previous authors has been done with the thermocouple method 
which involves piercing the insect. Is the vital temperature so re¬ 
corded any index of the capacity of the insect to resist low tem¬ 
perature? In order to test this, quiescent adults, pupae, and larvae 
were removed from the beans and 
put into a gelatin capsule through 
which the thermocouple point 
was thrust. The specimens were 
then uninjured and were lying 
around the couple point. The 
method was then modified in order 
to secure more rigidity by taking 
a piece of glass tubing, blowing a 
bulb at the end and then making a small hole in the bulb. The 
thermocouple was then thrust down until it was almost to the 
bottom of the bulb and the insects placed down in the bulb and 
close to the couple point. When several insects are so placed 
it so happens that one of them will “rebound,” but the heat 
given off will be dispersed and only a mere indication of the rebound 
will be recorded by the instrument. Rebound under these circum¬ 
stances then is simply an indication that inoculation has taken place 
and the amount is not significant (Table II). 
==o 
== 0 
Fig. 1.—Diagram of glass tube used in freezing 
insects without injury due to piercing by 
thermocouple 
Table II .—Experiments to determine the effect of injury on an insect’s resistance 
Super¬ 
cooling 
point 
Rebound 
point 
Stage 
Num¬ 
ber 
used 
Result 
°C. 
-13.60 
°C. 
-10.70 
Pupal... 
14 
All died. 
-17.00 
None. 
...do_ 
15 
Lived. 
-20.00 
None. 
...do_ 
3 
Do. 
-20.00 
None. 
...do- 
3 
Do. 
-20.00 
None. 
...do- 
3 
Do. 
-13.25 
None. 
Larval.. 
1 
Do. 
-16.50 
None. 
...do- 
1 
Do. 
-16.00 
None. 
...do_ 
1 
Do. 
-20.00 
None. 
...do- 
24 
Do. 
-17.00 
Slight. 
...do_ 
4 
Three lived.® 
-15.50 
None. 
...do_ 
1 
Lived. 
-17.00 
None. 
Adult 6 .. 
10 
Seven lived. 
-17.00 
None. 
...do. 6 _ 
15 
Six lived. 
-22.00 
None. 
...do. 6 _ 
10 
One lived. 
• Of these four larvae one was slightly injured putting it into the tube .and a thin film of its body fluid 
held it to the glass. The couple was not touching it. Only that larva died; the other three lived. 
6 Unemerged adults. 
