INSECT CONTROL IN FLOUR MILLS. 39 



RESULTS OF HEATING MILL NO. 5. 



All insects were killed on the second and third floors. Dead beetles and 

 larvae could be found beneath 3 inches of flour. All insects were killed on the 

 first floor except near air shaft (thermometer No. 1) and those buried 5 inches 

 in flour (thermometer No. 2). 



CONTROL BY FREEZING. 



If an infested mill is so equipped that it can be opened to low out- 

 door temperatures without injury to equipment, freezing is an inex- 

 pensive and valuable remedy for the flour moth. Turning off all 

 heat and opening the mill to a temperature of zero or lower for from 

 3 to 10 nights continuously, or at intervals, has often proved effective 

 in destroying the moth in its different stages. Mills in the northern 

 United States and in Canada, where temperatures of 20 to 30 degrees 

 below zero (Fahrenheit) are often experienced, have used this 

 method of control with good results. Mills located farther south 

 where freezing temperatures do not run so low or prevail continu- 

 ously for any length of time have had little or no benefit from at- 

 tempts to utilize cold weather. 



CONTROL BY SMUDGES. 



Control by means of smudges in the form of sulphur or tobacco 

 fumes, etc., is depended upon rather extensively in many mills to 

 reduce flour-moth injury. With smudges one can only expect to 

 reduce the flour moth temporarily by killing the adult moths and 

 certain of the immature stages. The fumes generated are not strong 

 enough to kill as do hydrocyanic-acid gas fumigation and high tem- 

 peratures. In rambling, loosely constructed buildings, where control 

 by heat and hydrocyanic-acid gas is not practical, smudges, coupled 

 with constant cleaning, have their value. The moth miller or adult 

 is the most easily lulled of the different stages of the flour moth and 

 is the form killed in largest proportions by smudges. Since each 

 female moth is the potential parent of several hundred larvae, one 

 can appreciate the value of the persistent use of smudges. The chief 

 drawback to dependence upon smudges is that they never completely 

 exterminate the moth. Smudges, to accomplish satisfactory results, 

 must be applied frequently, and are therefore costly in the long run. 

 One thorough application of heat rids a mill of the flour moth for 

 long periods if provision is made against reinfestation from without. 

 Flying moths may be found as soon as one day after the application 

 of a smudge. 



CONCLUSION. 



Control of insect pests in flour and cereal mills has become a very 

 important feature of food conservation and of mill construction and 

 operation. Losses caused by mill insects to mill owners and the ad- 



