August, '14] GOODWIN: HEAT CONTROL FOR MILL INSECTS 313 



SOME FACTORS AFFECTING RESULTS IN THE USE OF 



HIGH TEMPERATURE FOR THE CONTROL OF 



INSECTS INJURING CEREAL PRODUCTS 



By W. H. Goodwin 



In some experiments in treating flour mills using heat, several 

 failures were experienced when apparently sufficient radiation had been 

 installed. These mills had proportionally as much radiation as simi- 

 larly^ constructed mills in which excellent results had been obtained. 

 A careful survey of these mills failed to disclose any lack of steam 

 pressure; neither was the failure due to only partial circulation of 

 steam in the radiator coils; nor to a greatly reduced opening in the 

 steam pipes leading to the heating coils. In one or two mills a lack of 

 steam pressure owing to the small or greatly reduced passage ways of 

 the steam mains, or feed pipes, was readily discovered and the trouble 

 soon remedied. In two flour mills, however, leaks in the heating 

 coils produced an extremely moist atmosphere, and although the tem- 

 perature was high enough to kHl most of the stages of the Mediterran- 

 ean flour moth, especially the small larvae, many of the other minor 

 mill pests survived and appeared to be none the worse for having been 

 heated. The temperatures attained, 45°C. to almost 47°C., Avere 

 high enough to kill many of the insects present, but, apparently, on 

 account of the relatively" high humidity many survived. These insects 

 which survived the test were not greatly disturbed, even when the 

 duration of the heating period was greatly lengthened. The heated 

 atmosphere did not seem to penetrate very deeply into any collections 

 of flour which occurred in machines or in conveyors in which these 

 insects lived. The treated insects which survived acted perfectly 

 normal after the test, and reproduced normally later in the year. 

 This appeared to disprove the practical efficiency of high temperature 

 for the control of cereal insects, unless a greatly increased amount of 

 radiation was provided. 



The amount of radiation present, already exceeded the requirement 

 for similarly constructed flour mills, in which excellent results had been 

 obtained. The only factor which appeared to be responsible for the 

 extreme difference and that was preventing the necessary rise in tem- 

 perature above 45°C. to the fatal temperature for most insects, 48°C. 

 to 52°C., was the extreme humidity of the heated atmosphere. The 

 thermal conductivity of the wood floors being very small, the evapora- 

 tion was not rapid, but the amount of heat absorbed by the evaporating 

 water cooled the atmosphere in the mill being treated to such an ex- 

 tent that the necessary rise in temperature above 45°C. to the fatal 



