STUDIES OF THE PINK BOLLWORM IN MEXICO 
47 
The results of these tests are summarized in Table 39. All the 
tests with dry heat giving 100 per cent mortality, except those from 
145° F. down, were repeated three or four times. 
Table 39. 
■Thermal death point of pink bollworm larvae in double seed exposed to 
heat in Freas oven, with margin of safety for seed 
Period 
of 
exposure 
Temperature re- 
quired to cause 
100 per cent mor- 
tality 
Maximum tem- 
perature to which 
seed may be 
heated without 
injury to germi- 
nation 
Dry air 
Moist air 
Dry air 
Moist air 
Minutes 
5 
10 
15 
20 
30 
45 
60 
O p 
195 
170 
o F 
160 
145 
•■* 
o p 
175 
170 
145 
140 
135 
130 
135 
130 
125 
165 
170 
160 
160 
In the tests with the larvae in seed more heat was required than 
Willcocks u found necessary in his experiments. With dry air he found 
a 30-minute exposure at a temperature ranging from 121 to 129° F. 
to give 100 per cent mortality, and with moist air an exposure for 
4 minutes at 159.8°. This difference is probably due to the fact that 
Egyptian seed is practically devoid of lint. 
Following the tests that are given in Table 39, a series of experi- 
ments with unprotected larvae was conducted in the Freas oven. 
These experiments differed further from the others in the fact that 
the larvae were placed in the oven at approximately air temperature, 
and the temperature afterward raised. Two devices were finally 
decided upon as giving the most accurate results. The first was to 
place the larvae in a cylindrical screen cage with a cardboard floor 
in the center, on which the larvae rested. A thermometer was in- 
serted centrally through this cylinder with the bulb partly above 
and partly below the cardboard floor. This cage with thermometer 
in position was hung in the oven and kept swinging like a pendulum 
until the desired temperature was reached. Then it was removed 
and the larvae immediately cooled. In the second device the larvae 
were placed in a shallow perforated blotter tray in the bottom of 
which a thermometer rested. The tray was set in the oven and the 
temperature raised until the desired point was reached. Then the 
tray was removed and the larvae immediately cooled. The results of 
the tests conducted in these two ways are given in Tables 40 and 41. 
" F. C. Willcocks. Op. cit. 
