40 BULLETIN 872, U. S. DEPARTMENT OF AGRICULTURE. 



vantages of modern mill construction are working hand in hand to 

 bring about a constant change for the better. Putting into practice 

 methods of control advocated in this bulletin will make it possible 

 for milling concerns to place upon the market a product reasonably 

 free from infestation. When insect sanitation is conscientiously ap- 

 plied, millers can state that blame often heaped upon them by brokers, 

 retail grocers, and the public at large is due to one or more of several 

 known conditions connected with warehousing and transportation, 

 for the miller is in no way responsible. 



There are a number of serious insect pests of flour mills. The long- 

 established pests in American mills do not interfere noticeably with 

 operation of mill machinery. With the spread from Europe to the 

 United States of the Mediterranean flour moth (p. 2-5), millers 

 were forced to consider insect sanitation. The danger in the flour 

 moth, sometimes called the " gray plague of flour mills," does not lie 

 so much in food values actually consumed as in the enormous quanti- 

 ties of silken threads spun by its larvae in and about mill machinery. 

 This webbing habit causes the flour in passing through the machinery 

 to form in ever-increasing clumps or webbed masses, which sooner 

 or later choke or clog the machinery, and necessitates extensive mill 

 shutdowns for cleaning and application of control measures. 



Experimental and practical demonstration work has proved the 

 dependability of methods of control under certain conditions. These 

 are fumigation with hydrocyanic- acid gas and the use of heat. Con- 

 trol by freezing (p. 39) is less satisfactory. Smudges, as com- 

 pared with fumigation with hydrocyanic-acid gas or the applica- 

 tion of high temperatures, have only a temporary value. Preventive 

 measures, including cleanliness, are of the greatest value in reducing 

 losses due to insects. Dependence upon natural control by parasites 

 is not advocated. The heat method is recognized as the most effective, 

 practical, and inexpensive of all treatments and has the added ad- 

 vantage of being absolutely safe. Where remedial measures must be 

 applied in mills of moderate size, it has been estimated that the heat 

 method is enough cheaper to pay in five years for the cost of the 

 installation of enough radiation surface properly to heat the mill. 



Neither fumigation with hydrocyanic-acid gas nor the use of high 

 temperatures, as recommended for mill-insect sanitation, injures the 

 mill building or equipment or affects the baking qualities of flour. 



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