COTTON 395 



It has been impossible to find a satisfactory system 

 of dealing- with the pink boll worm after the cotton seed 

 has been sacked. If any treatment is to be applied 

 successfully the seed must be loose, whether in large or 

 in small quantities. 



The best 'results have been obtained from the following" 

 methods : 



(i) Hot-air Treatment. It was anticipated and proved 

 to be correct that there is a difference in the temperatures 

 necessary to kill Gelechia larvae and cotton seed. A 

 practical temperature under o C. was not found; on the 

 other hand, the worms cannot exist at 50 C. for longer 

 than is required to heat them through and through to that 

 temperature. Cotton seed, on the other hand, will under- 

 normal conditions remain unaffected if thoroughly warmed 

 up to 65 C., and possibly up to 75 C. However, both 

 worms and seed can stand much higher temperatures for 

 short periods, the rule being, the higher the temperature 

 the shorter the period, and total mortality occurs amongst 

 tlie worms long before the seed suffers. 



In treating seed with hot air it was found necessary, 

 if uniform results were to be obtained, to spread out the 

 seeds in a 'single layer, in order to give the heated air 

 access to every single seed. Other factors to be con- 

 sidered were the heat conductivity of the material on 

 which the seeds were carried, the initial temperature oi 

 the seed, the temperature employed, and the time of the 

 exposure. The seed must not previously have been 

 wetted, or wetted and dried. In order to kill the worms 

 and not to hurt the seed, it was necessary to adjust all 

 these factors, which could be adjusted in the machine 

 used, in such a way that the worms and seed should 

 reach a minimum temperature throughout of about 55 

 to 60 C. The material of the carrier would normally 

 be a constant, the depth of the seed layer also. The 

 initial temperature of the seed in our experiments was 

 not considered, as it would not have varied more than 

 one or two degrees from 15 C., that being the tempera- 

 ture of our laboratory. In the practical application of 

 the hot-air treatment the initial temperature of the seed 

 might become important, as it could conceivably vary by 



