﻿STUDIES OF THE PINK BOLL.WORM 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 p 



160 

 145 



p_ 



o p 







175 



170 



145 

 140 

 135 

 130 



135 

 130 



125 



165 



170 



160 



160 





In the tests with the larvse in seed more heat was required than 

 Willcocks " found necessary in his experiments. With dry air lie 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 

 Eg}-^tian seed is practically devoid of lint. 



Following the tests that are given in Table 39, a series of experi- 

 ments with unprotected larvaB 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 

 ))lace 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 tlie 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 tJic 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. clt. 



